Fix layout & transparency issues with incoming call UI

Tested, confirmed, fabulous.

PS5: Rebased. #APCONFIRMED #HOLOYOLO
PS6: Restored the non-transparent case to R.colors.incall_call_banner_background, and the transparent case to R.color.transparent

Change-Id: I4d16241ddd7f4fc5af7ee9a6195a378daf3c5265