KeyboardLayoutPickerFragment uses DashboardFragment

- Build a controller to generate a list of preferences and add to screen.
- Move some logic to controller.
- Add some test cases for controller.

Test: manual
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.inputmethod
      make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.core
      make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.dashboard
      atest UniquePreferenceTest
Change-Id: I4ebe486ade3439b9814b11866c402dcf881f21a7