viewer: migrate to vue 3, general refactoring and cleanup

Non-exhaustive list of fixes and improvements done at the same time:

- html default background to grey (avoids white flash during init)
- unified links behavior
- added more theme variables
- removed the flex-expand transition (it wasn't working) and replaced it
  with a slide
- fixed LdLoading not centered on the content
- title on removable tags
- fixed an issue with encoded URI from vue-router
- unified Item resource URLs
- removed the iframe for PlainTextViewer (it wasn't working properly)
  and replaced it with a pre
- fixed clear and search buttons tabindex
- fixed the information panel bumping up during the fade animation of
  tag's dropdown
- fixed some focus outlines not appearing correctly
- moved CSS variables to the :root context
- Code cleaning

GitHub: closes #217
GitHub: closes #300
GitHub: closes #297
GitHub: closes #105
GitHub: closes #267
GitHub: closes #275
GitHub: closes #228
GitHub: closes #215
GitHub: closes #112

24 files changed, 185 insertions, 1484 deletions

diff --git a/viewer/src/components/LdBreadcrumb.vue b/viewer/src/components/LdBreadcrumb.vue
deleted file mode 100644
index d518365..0000000
--- a/viewer/src/components/LdBreadcrumb.vue
+++ /dev/null
@@ -1,129 +0,0 @@
-<!-- ldgallery - A static generator which turns a collection of tagged
---             pictures into a searchable web gallery.
---
--- Copyright (C) 2019-2020  Guillaume FOUET
---
--- This program is free software: you can redistribute it and/or modify
--- it under the terms of the GNU Affero General Public License as
--- published by the Free Software Foundation, either version 3 of the
--- License, or (at your option) any later version.
---
--- This program is distributed in the hope that it will be useful,
--- but WITHOUT ANY WARRANTY; without even the implied warranty of
--- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
--- GNU Affero General Public License for more details.
---
--- You should have received a copy of the GNU Affero General Public License
--- along with this program.  If not, see <https://www.gnu.org/licenses/>.
--->
-
-<template>
-  <div
-    ref="breadcrumb"
-    v-dragscroll
-    class="flex scrollbar"
-    :class="$style.ldBreadcrumb"
-    @click.capture="e => dragScrollClickFix.onClickCapture(e)"
-    @dragscrollstart="dragScrollClickFix.onDragScrollStart()"
-    @dragscrollend="dragScrollClickFix.onDragScrollEnd()"
-    @dragscrollmove="checkForOverflowMask"
-  >
-    <div v-show="overflowMask" :class="$style.ldBreadcrumbOverflowMask"></div>
-    <ul>
-      <li v-for="(item, idx) in currentItemPath" :key="item.path">
-        <fa-icon v-if="idx > 0" icon="angle-right" class="disabled" />
-        <router-link :to="item.path" class="link">
-          <fa-icon :icon="getIcon(item)" size="lg" />
-          {{ item.title }}
-        </router-link>
-      </li>
-      <li v-if="searchMode">
-        <fa-icon icon="angle-right" class="disabled" />
-        <router-link :to="$route" class="link">
-          <fa-icon icon="search" size="lg" class="disabled" />
-        </router-link>
-      </li>
-    </ul>
-  </div>
-</template>
-
-<script lang="ts">
-import { Item } from "@/@types/gallery";
-import DragScrollClickFix from "@/services/dragscrollclickfix";
-import Navigation from "@/services/navigation";
-import { Component, Prop, Ref, Vue, Watch } from "vue-property-decorator";
-
-@Component
-export default class LdBreadcrumb extends Vue {
-  @Prop({ type: Array, required: true }) readonly currentItemPath!: Item[];
-  @Prop(Boolean) readonly searchMode!: boolean;
-  @Ref() readonly breadcrumb!: HTMLUListElement;
-
-  readonly dragScrollClickFix = new DragScrollClickFix();
-
-  dragging: boolean = false;
-  overflowMask: boolean = false;
-
-  mounted() {
-    window.addEventListener("resize", this.checkForOverflowMask);
-  }
-
-  destroyed() {
-    window.removeEventListener("resize", this.checkForOverflowMask);
-  }
-
-  checkForOverflowMask() {
-    this.overflowMask = this.breadcrumb.scrollLeft > 1;
-  }
-
-  @Watch("currentItemPath")
-  changedCurrentItemPath() {
-    this.$nextTick(() => {
-      this.breadcrumb.scrollLeft = this.breadcrumb.scrollWidth;
-      this.checkForOverflowMask();
-    });
-  }
-
-  getIcon(item: Item) {
-    return Navigation.getIcon(item);
-  }
-}
-</script>
-
-<style lang="scss" module>
-@import "~@/assets/scss/theme.scss";
-
-.ldBreadcrumbOverflowMask {
-  position: absolute;
-  width: 100%;
-  height: 100%;
-  background: linear-gradient(
-    to right,
-    rgba($panel-top-bgcolor, 1) $breadcrumb-margins,
-    rgba($panel-top-bgcolor, 0) $breadcrumb-overflow-mask-size
-  );
-  pointer-events: none;
-}
-
-.ldBreadcrumb {
-  ul {
-    display: flex;
-    white-space: nowrap;
-  }
-  a {
-    padding: $breadcrumb-margins 0;
-    margin-left: $breadcrumb-margins;
-  }
-  li {
-    align-self: center;
-    margin-right: $breadcrumb-margins;
-  }
-  &:global(.scrollbar) {
-    overflow-y: hidden;
-    scrollbar-width: none;
-    &::-webkit-scrollbar {
-      height: 0;
-    }
-  }
-}
-</style>
diff --git a/viewer/src/components/LdCommand.vue b/viewer/src/components/LdCommand.vue
deleted file mode 100644
index 19174ad..0000000
--- a/viewer/src/components/LdCommand.vue
+++ /dev/null
@@ -1,98 +0,0 @@
-<!-- ldgallery - A static generator which turns a collection of tagged
---             pictures into a searchable web gallery.
---
--- Copyright (C) 2019-2020  Guillaume FOUET
---               2020       Pacien TRAN-GIRARD
---
--- This program is free software: you can redistribute it and/or modify
--- it under the terms of the GNU Affero General Public License as
--- published by the Free Software Foundation, either version 3 of the
--- License, or (at your option) any later version.
---
--- This program is distributed in the hope that it will be useful,
--- but WITHOUT ANY WARRANTY; without even the implied warranty of
--- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
--- GNU Affero General Public License for more details.
---
--- You should have received a copy of the GNU Affero General Public License
--- along with this program.  If not, see <https://www.gnu.org/licenses/>.
--->
-
-<template>
-  <div class="flex" :class="$style.commandBtns">
-    <a class="link" :title="$t('command.search')" @click="$uiStore.toggleFullWidth()">
-      <fa-icon :icon="commandToggleSearchPanelIcon" size="lg" />
-    </a>
-    <ld-command-sort />
-    <a
-      class="link"
-      :class="{ disabled: isEntryPoint(), [$style.commandSecondary]: true }"
-      :title="$t('command.back')"
-      @click="isEntryPoint() || $router.back()"
-    >
-      <fa-icon icon="arrow-left" size="lg" />
-    </a>
-    <router-link :class="{ disabled: isRoot }" :title="$t('command.parent')" :to="parent">
-      <fa-icon icon="folder" size="xs" />
-      <fa-icon icon="level-up-alt" size="lg" />
-    </router-link>
-  </div>
-</template>
-
-<script lang="ts">
-import { Item } from "@/@types/gallery";
-import { Component, Prop, Vue } from "vue-property-decorator";
-import { RawLocation } from "vue-router";
-
-@Component
-export default class LdCommand extends Vue {
-  @Prop({ type: Array, required: true }) readonly currentItemPath!: Item[];
-