Rework how we decide whether to use system or status bar.

The PhoneWindowManager is now responsible for determing this,
since it needs to do this before we can generate the configuration
since we need to take into account the system bar size we will use.

Also the Display should now report the screen height without
including the system bar.

Change-Id: I82dfcc5e327e4d13d82c373c6c870f557a99b757