[Settings] long press back to kill with configurable timeout (2/2)

1 - 2 seconds (default)
2 - 1,5 seconds
3 - 1 second
4 - 0,5 second

PS: ONLY IN NAVIGATION BAR LONG PRESS BACK. STILL NEEDS TO BE IMPLEMENTED IN PIE

Change-Id: I7ee1a1918150e5dbcdc04e2b325d9fce5b4d9cf6