frameworks: allow last app action to be assigned to hardware keys

Also fix multi-user handling for 'switch to last app' and 'kill
foreground app' actions.

Change-Id: I1fb586d19b1198e6888b0f11e0a2813acf0bcd5b
Signed-off-by: Roman Birg <roman@cyngn.com>
Signed-off-by: Danny Baumann <dannybaumann@web.de>
Signed-off-by: Adnan Begovic <adnan@cyngn.com>

Conflicts:
	core/res/res/values/symbols.xml
	policy/src/com/android/internal/policy/impl/PhoneWindowManager.java