Add headless mode for running the framework without the surface flinger

Enabled by setting system property ro.config.headless to 1
This will allow the framework to run without starting activities,
system UI and the keyguard.
Framework can still run services, content providers and broadcast receivers.

Signed-off-by: Mike Lockwood <lockwood@android.com>

Conflicts:

	policy/src/com/android/internal/policy/impl/PhoneWindowManager.java
	services/java/com/android/server/PowerManagerService.java
	services/java/com/android/server/am/ActivityManagerService.java