Fix recent emoji sort order

The recent emoji tab was sorting emoji as last in last out instead
of last in first out. Also, if an emoji was already in the recent
emoji cache its order would not be updated on reinsert.

Fixes #2967
Closes #2946

// FREEBIE

src/org/thoughtcrime/securesms/util/Emoji.java

@@ -263,7 +263,8 @@ public class Emoji {
   }
 
   public Pair<Integer, Drawable> getRecentlyUsed(int position, double size, PageLoadedListener pageLoadedListener) {
-    String code = EmojiLRU.getRecentlyUsed(context)[position];
+    String[] recentlyUsed = EmojiLRU.getRecentlyUsed(context);
+    String   code         = recentlyUsed[recentlyUsed.length - 1 - position];
     return new Pair<Integer, Drawable>(Integer.parseInt(code, 16), getEmojiDrawable(code, size, pageLoadedListener));
   }
 
@@ -329,6 +330,7 @@ public class Emoji {
         prefs = PreferenceManager.getDefaultSharedPreferences(context);
       }
 
+      recentlyUsed.remove(asset);
       recentlyUsed.add(asset);
 
       if (recentlyUsed.size() > EMOJI_LRU_SIZE) {