[3/3] InCallUI: allow disabling non intrusive incall ui

Change-Id: I86bd4b46f031004fa90f1d7936263f9dabcd3860
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
InCallUI: fix non intrusive incallui layout

- makes the decline/answer buttons evenly sized
- decrease font size of buttons to 13sp so the non-english button labels fit better

before: https://www.dropbox.com/s/g9mn72qhzq6wlbt/2014-01-01%2006.00.31.png
after:  https://www.dropbox.com/s/dfhmaliz6a21lk5/2014-01-01%2010.30.42.png

Change-Id: I88e0f0a1358595f2ce86dddcae2ab4d4e788fc1a
InCallUI: fix non-intrusive for RTL

http://jira.omnirom.org/browse/OMNI-522

Change-Id: Ib712ccc2c207e329bdfa4cf64d29f2aeb130f59b