Major refactor of ConversationCursor

* ConversationCursors are now associated with a particular loader;
  there are no static methods or static state fields
* ConversationCursorLoader maintains a list of current loaders
  (for tracking/debugging)
* AbstractActivityController acts as a router of conversation
  changes to/from fragments (currently message view -> conversation
  list)
* Comment out some ConversationCursor tests for now

Change-Id: I9b8425a19c77501796b6681142e1bc0ad20b3693
24 files changed