Android: Refactor Story Loading

This is the big refactor of story loading.  We no longer blindly blow away the DB and restart at API page 1 at the drop of a hat (switching screens, running out of pages, rotating the screen, etc).  We now start with a clean slate and load on demand or when filters change only.  Much cleanup ensued.  Also did more bug-chasing to deal with the new async story fetching.

As a result of all this, I'm actually confident now that we don't have to rush the addition of a DB column to track read-during-session status.  This build seems to have eliminated most of the remaining bugs, save for those caused by the rotation bug in reading view.

Additionally, fixed the race condition that was causing the Next Unread button not to work.  However, this fix *will not work on pre-3.0 devices*.  Before we lauch this, we should update the manifest appropriately.