Extract the twilight detection into its own service.

Moving the detection out of UiModeManagerService will
make it easy for other services to register for the
information.

Fixed a bugs related to updating twilight state
when the time is updated.

We're using the same algorithm as before for passively
tracking the location.  Ideally we should update it
to use the new location manager features for low-power
location requests.

Change-Id: I520c53b9946ab6f8d994587d357fd6542c300c07