Implement issue # 3255887 could CursorLoader offer...

...to throttle contentobserver-based requeries

Why yes, I guess it could.

This also reworks AsyncTaskLoader to not generate multiple
concurrent tasks if it is getting change notifications before
the last background task is complete.

And removes some of the old APIs that had been deprecated but
need to be gone for final release.

And fixes a few little problems with applying the wrong theme
in system code.

Change-Id: Ic7a665b666d0fb9d348e5f23595532191065884f