Added icon to change-playlist btn

app/views/templates/change_playlist.scala.html

 @(playlists:List[String])
 <button class="button dropdown" type="button"
-  data-toggle="playlist-dropdown">Change Playlist</button>
+  data-toggle="playlist-dropdown"><li class="fi-list-numbered"></li>Change Playlist</button>
 
 <div class="dropdown-pane" id="playlist-dropdown"
   data-dropdown data-auto-focus="true">