settings: Add support for SRE

 * Add support for sunlight readability enhancement
 * Optionally depends on adaptive backlight, depending on HAL

Change-Id: I9ca388ffd68080f0e497edb81d5f8616c194ea1d
Revert "Allow changing theme to Holo.Light without crashing"

http://review.cyanogenmod.org/#/c/70745/ solves the issue
that this patch originally was created for.

This reverts commit 8cc23d58abc4874fe049a8dfa70910cf0b5dd9b2.

Change-Id: Ia350a03749202a2c0ae809400a3ebb554551d601
Settings: add last app action to be assigned to hardware keys