Add never sleep screen mode [1/2]

to qs ScreenTimer Tile
to PW ScreenTimer toggle
as general option as well

Change-Id: Ic78356c1b96044562efbce3cb0d0d5c93d773a19

Conflicts:
	packages/SystemUI/res/values/slim_strings.xml
	packages/SystemUI/src/com/android/systemui/quicksettings/ScreenTimeoutTile.java
	packages/SystemUI/src/com/android/systemui/statusbar/powerwidget/ScreenTimeoutButton.java