InCallUI: Heads up meets N5X... N5X meets Google IO [2/4]

Add native heads up support on dialer.

We only have show call in background feature. We combine it now with heads up.
So it is doing exactly same like on Google IO was shown.

Enabled by default.

- Notification is expanded by default
- Send as requested to force show the heads up no matter what.

Change-Id: I819316226f990058e6da6c289b8424d80ac1456e