Support for different themes

Weekeyboard now checks the its config to decide which theme to load. Themes can
also be changed during runtime.

Change-Id: I84dcbfd0b1d7aadb55c33aa2c00f1f15fd280670
Patch-by: Robert Erickson <rerickso@jaguarlandrover.com>
Signed-off-by: Eduardo Lima (Etrunko) <eduardo.lima@intel.com>