Add setting for system bars visibility on Keyguard in Expanded desktop mode.

And combine expanded settings into a category.

Change-Id: I8e5a718faae002280da37cdd68e292f01648751b
Merge "Add setting for system bars visibility on Keyguard in Expanded desktop mode." into cm-11.0
Merge remote-tracking branch 'cm/cm-11.0' into cm-11.0