Overflow menu for action bars.

The overflow menu replaces the normal options menu panel for
activities with an action bar. It always appears as the rightmost
action button and is displayed as a dropdown menu. The menu key
summons and dismisses the overflow menu instead of the options panel
where applicable.

Change-Id: I0b4fa7e36f35ab12e2f0c1d12bec79ccab8cc4b1