[2/2] omnigears: add custom hardware button mapping

Possible mapping

 0 - Nothing
 1 - Menu
 2 - App-switch
 3 - Search
 4 - Voice search
 5 - In-app search
 6 - home
 7 - back
 8 - toggle last app
 9 - kill app

Overlays required
<bool name="config_has_hardware_buttons">true</bool>

PS2/3:
whitespace cleanup

PS4:
layout rework

PS7:
added home action check and alert
changed enable to switch

PS8
fixed change to switch

Change-Id: I3b8b3bbd31b416d0952acd1f9a86cdd28a8002e5