(2/4) InCallUI: real non intrusive UI

this time attach it to the window manager as overlay instead of
opening a semi transparent fake activity

the dialog can also be dragged down to be even more non intrusive, called
full non intrusive i guess

thanks to @omnirom for the initial commit of the non intrusive incall

Change-Id: I949cc025f26348e2b8aee71a6276deb3bcc97903