[web] Rewrite of the GroupedList to accept multiple sort criteria

web-src/src/components/ListAlbums.vue

@@ -2,9 +2,9 @@
   <template v-for="album in albums" :key="album.itemId">
     <div v-if="!album.isItem && !hide_group_title" class="mt-6 mb-5 py-2">
       <span
-        :id="'index_' + album.groupKey"
+        :id="'index_' + album.index"
         class="tag is-info is-light is-small has-text-weight-bold"
-        v-text="album.groupKey"
+        v-text="album.index"
       />
     </div>
     <div

web-src/src/components/ListArtists.vue

@@ -3,9 +3,9 @@
     <div v-if="!artist.isItem && !hide_group_title" class="mt-6 mb-5 py-2">
       <div class="media-content is-clipped">
         <span
-          :id="'index_' + artist.groupKey"
+          :id="'index_' + artist.index"
           class="tag is-info is-light is-small has-text-weight-bold"
-          v-text="artist.groupKey"
+          v-text="artist.index"
         />
       </div>
     </div>

web-src/src/components/ListComposers.vue

@@ -3,9 +3,9 @@
     <div v-if="!composer.isItem && !hide_group_title" class="mt-6 mb-5 py-2">
       <div class="media-content is-clipped">
         <span
-          :id="'index_' + composer.groupKey"
+          :id="'index_' + composer.index"
           class="tag is-info is-light is-small has-text-weight-bold"
-          v-text="composer.groupKey"
+          v-text="composer.index"
         />
       </div>
     </div>

web-src/src/components/ListGenres.vue

@@ -3,9 +3,9 @@
     <div v-if="!genre.isItem && !hide_group_title" class="mt-6 mb-5 py-2">
       <div class="media-content is-clipped">
         <span
-          :id="'index_' + genre.groupKey"
+          :id="'index_' + genre.index"
           class="tag is-info is-light is-small has-text-weight-bold"
-          v-text="genre.groupKey"
+          v-text="genre.index"
         />
       </div>
     </div>

web-src/src/components/ListTracks.vue

@@ -2,9 +2,9 @@
   <template v-for="track in tracks" :key="track.itemId">
     <div v-if="!track.isItem" class="mt-6 mb-5 py-2">
       <span
-        :id="'index_' + track.groupKey"
+        :id="'index_' + track.index"
         class="tag is-info is-light is-small has-text-weight-bold"
-        v-text="track.groupKey"
+        v-text="track.index"
       />
     </div>
     <div