Add selection, navigation and context menus to FeedListPage and have the feeds sorted
Selection, navigation and context menus are implemented similar to the implementation for entry lists.
The feed list is be sorted by (1) descending number of unread/unplayed entries and (2) alphabetically by name. The current item and current selection are maintained after re-sorting when the number of unread entries has changed.
Solves #9 (closed)