add support for overriding build.prop settings.

Change-Id: Ie4224d608b7bcb0c2087bd77bc954f8f5f9b6495

Conflicts:

	core/Makefile
Allow prebuilt apks & don't build calendar

Change-Id: I2b76f6d5131204b48ac101156f0cd861a3336807
Don't build magic wallpapers
Don't use sample apns
Fix device asserts