[3/3] InCallUI: Incoming Call in Background

Patch ported from 4.2 which was done by our lovely HCP. A
very popular one so we bring it back and adapt it to 4.4

Allows user to set that Incoming Call UI will remain in background
if screen is on. Instead, a notification is added to StatusBar, which
can be used to bring up the Incoming Call UI. Ringtone and vibration
still occur as per system settings.

This has the same effect as apps marked as "immersive". It prevents
the incoming call from backgrounding the current activity.

PatchSet:
- show normal inCallUI if keyguard is currently active

PS:
- cleanup

PS
- do not try to get the services if the feature is disabled

PS:
- do not disable notificationshade and navbar if it is a background call

InCallUI: add decline and answer incoming call action on notifications

Add decline and answer call action on notification if an call is incoming. Especially
usefull for call in background feature to have the ability to directly
decline or answer a incoming call. But as well usefull to decline/answer a second call
during one is incomming.

PS:
- found a better way for the answer button

PS:
- fix keep flip action alive
- fix collapse notification shade when answering call
- answer call before starting the UI to do not have
  shown the incall screen for a brief second

PS:
- fix wrong user on sending close system dialogs

InCallUI: Set Ticker to contact

Display contact/number/confrence
	in notification ticker.

PS2:
Implement Kufikugel's suggestion.
	Incoming call ticker only.

Change-Id: Ie89cceb67aecbf3dd15abd07dc35110f7fddc2f9