Make incall screen glopad background themeable

Change-Id: I6a0a120662e4e45b5282a763c8ccf41d29c6d470
InCallActivity: consume back key on incoming call screen

Users will not be able to anything if the physical back key is
pressed on the incoming call screen (return to home screen with
nothing responding.)

Forward porting the key consumption from 4.3

Change-Id: Iea0734852bac7ca5a25e19ec9d9ee7c80dba6741