Easy way to play current audiobook

This patch implements a generic way of re-opening the player for the
book you last listened to. This is especially handy when first opening
the app and you can restart playback with a single click.

The player is opened only if no other book is already open in the
player. It will not overwrite or replace playbacks or player already in
progress.

The player is opened paused. No automatic playback since that could be
really annoying.

This closes #494

pages/bookshelf/index.vue

@@ -247,6 +247,15 @@ export default {
           return cat
         })
 
+        // If we don't already have a player open
+        // Try opening the first book from continue-listening without playing it
+        if (!this.$store.state.playerLibraryItemId) {
+          const lastListening = categories.filter((cat) => cat.id === 'continue-listening')[0]?.entities?.[0]?.id
+          if (lastListening) {
+            this.$eventBus.$emit('play-item', { libraryItemId: lastListening, paused: true })
+          }
+        }
+
         // Only add the local shelf with the same media type
         const localShelves = localCategories.filter((cat) => cat.type === this.currentLibraryMediaType && !cat.localOnly)
         this.shelves.push(...localShelves)