Add global action bar menu.

This menu will be displayed when the navigation drawer is open.
Add beginning of mode switch framework.

This commit includes a method for swapping fragments on mode switches and
basic code for switching to the Lexicon Browse and Lexicon Favorites modes.
Add remaining fragments and swap code.
Add remaining fragment swapping code.

This commit also contains code to ensure that list items are highlighted in
two-pane mode.
Preserve action bar title on orientation change.