CM11 Themes: Allow defining a custom default theme [1/3]

Change-Id: I6b794d6c9c27b2d6436bdf4fec51c84a7859c134

Conflicts:
	packages/SettingsProvider/res/values/defaults.xml
	packages/SettingsProvider/src/com/android/providers/settings/DatabaseHelper.java
	services/java/com/android/server/SystemServer.java