Settings: Gamma calibration tunables

- Add support for negative values to gamma.
- Remove logs.

Change-Id: Ie06bf68bbc8e875d36966ed7f98a6beadb0169cc
Merge "Settings: Gamma calibration tunables" into cm-10.2
Merge branch 'cm-10.2' of git://github.com/CyanogenMod/android_packages_apps_Settings into cm-10.2