Phone: Add transparency to incall screen

Makes the background of multiview semitransparent.
It allows to at least see whole image of incoming caller.

Original commit: https://github.com/AOKP/packages_apps_Phone/commit/0a4c57816f55f6c0a1fbff457d2ccabc81e8f9e6

Change-Id: I920fee43e3bac7492a54f43281716eb8b686aa5e

Conflicts:
	res/layout/answer_fragment.xml
[1/2] InCall: Add a non-intrusive dialog for incoming calls

Change-Id: I7c8b5cc5138a5543be30579e99bd9989624e2abe
[3/3] InCallUI: allow disabling non intrusive incall ui

Change-Id: I86bd4b46f031004fa90f1d7936263f9dabcd3860