Keep keyboard lit until the screen is dimmed

Do not use button timeout for keyboard (which is intrusive on QWERTY
sliders). Keep it lit until the screen dims instead of turning it off
like the buttons after 5 seconds. Also consider setting keyboard
visibility as a user activity.

Conflicts:
	services/java/com/android/server/power/PowerManagerService.java

Change-Id: I32ea85ef558a5d3b5047695464e4172d24b3121d