SetupWizard: Add device specific hook page

* Add a new activity DeviceSpecificActivity which acts as a jumppad
  into an activity using "org.lineageos.settings.device.SUW_SETTINGS"
  * Handles navigation (back / next)
  * Handles cases where the script contains the page but SUW_SETTINGS
    don't exist
* In order to use this, devices need to provide an activity that:
  * at least shows a back and continue button
  * returns Activity.RESULT_OK and Activity.RESULT_CANCELLED for the
    buttons
  * does whatever you need to specifically have done in setup!

Change-Id: I4956c8f5f1ad13b9adf2e5604fd4a728e261336b