Move launch default activity prompt to the menu

Instead of asking at startup, the prompt now launches from a menu item.
This also get's rid of the snackbar because it was causing bugs with
rotation.

Furthermore now the android.permission.SYSTEM_ALERT_WINDOW permission is
no longer needed.

Test: Manual
Change-Id: I566e58d4844aecf127b5198c050ff115de7e4919