Add KitKat wifi and battery icons.

This adds wifi and battery icons for Gingerbread and KitKat. This also
improves the icon resolution code by extracting it out in its own class.
The resources are now organized such that each API level resource
directory is used as a backup for all API levels lower than itself.

Change-Id: I937c83638adcc9fa8cd407e0a3023c3abe95530d