Create Settings app object

Migrate airplane mode, bluetooth and cell data settings tests to the app

This is the beginning of migrating the settings tests to a settings app. This introduces the private ```_tap_menu_item``` method which contains the appropriate wait for the menu to slide into place. This will allow us to move any existing code using tap(target), and will increase the reliability of many of the settings tests.

After this is reviewed and ready to be merged I will tackle the other tests that use the settings app.