Overhaul auto-brightness level UI.

This changes a few things:
- Don't imply a 'bucket' type of algorithm is used by showing an ambient
  brightness range for each line
- Allow manually entering the screen brightness
- Add a preview window for the cubic spline interpolation
- Add a help text

Change-Id: I64274280872b9fe4f6fdc368d654aca81e0a4e0c
Signed-off-by: Dan Trifan <jimsth@gmail.com>
Correctly restore brightness customize dialog hierarchy.

This is especially important when rotating the device.

Change-Id: Iaf1ceb46943e9d0a171d6a75d3d446dbec205095
Signed-off-by: Dan Trifan <jimsth@gmail.com>