Settings: Add per app controls for LP keyguard notifications (2/2)

Nice done by google but the UX is a problem especially for ppl who are using a lot apps and just want
to see from important apps the notifications on the lockscreen.

This commit adds the ability to

- enable/disable per app the keyguard notification at all
- enable/disable per app ongoing notifications on the keyguard

We handle this over the app policy conf file like the other per app notification options

Change-Id: Ie4966f9048718c080571935796258625413f7344

Conflicts:
	res/values/slim_strings.xml