Re-add auto brightness configuration UI (1/2)

- Add a button into the new brightness dialog that allows opening the
  auto brightness setup
- Enable auto-brightness adjustment (setting for general brighter/darker
  adjustment) and twilight adjustment

Change-Id: I7fd11ddaa112396dcb7508692aacb93bfe3da256
Add method to PowerManager that allows querying the lowest possible
brightness.

Used by the auto-brightness adjustment to adjust the sliders.

Change-Id: Idb58fd86dee1a053fe858291be6c9b3169ac4247
Fixed autobrightness derp

Change-Id: I5090c985095cd63d4af191add78877485d7ea5c7