Performance: Add low RAM option (1/2)

* Allow users to choose between more free RAM available vs full KitKat UI features
* Fix zRAM option not set when ro.zram.default is null

Change-Id: I4066ec6ab450942abe654fa75062a471b0f8a4b6
Merge branch 'cm-11.0' of https://github.com/AORP/android_packages_apps_Settings into cm-11.0