Add back backlight curve adjustment.

Patch set 1-8: Initial commits
Patch set 9  : Shortened strings to better fit Design Guidelines

Change-Id: I1eb370f8911d1c92ef06e553cc1c1be81e83cb95
Some post-merge cleanup for automatic brightness adjustment

- Remove some unused strings
- Use (device-dependant) minimum brightness level (as calculated by
  DisplayPowerController) as '0%' instead of the actual value 0.

Change-Id: I79123d2421c9ab35fa0f1808d82d785463e8fbaa