Add a ImageListFragment activity.  Currently it is set as the default activity to load.
Still need to:
 - Improve the layout, currently it is bare bones.  Need to add post information to the list items including subreddit (only for the 'All' or multi-subreddits), number of comments, and maybe the ability to tap an image and see a quick full-screen preview without loading the whole ViewPager.
 - Add support for toggling between ListView/GridView modes.
 - Fix loading of default subreddit list as well as subscribed reddits for logged in users.