Refactor airplane mode preference controller.

- Convert inheritance from AbstractPreferenceController to
TogglePreferenceController.
- Register AirplaneModePreferenceController in XML.
- Decouple AirplaneModeEnabler with preference, leave the UI be
controled by PreferenceController.
- Add RoboTests test cases for AirplaneModePreferenceController.

Fixes: 67997339
Test: RunSettingsRoboTests
Change-Id: I7398943ed51345e014ee7aa774bfae1ca28632f1