Dialer: Fix settings

* RingtonePreference doesn't exist in androidx world - we have to
  make our own
* We don't need to remove the dividers anymore - androidx doesn't have
  them in the first place
* AppCompatPreferenceActivity is deprecated as well, make it
  an AppCompatActivity and start using fragments

Change-Id: I54d22868deb8950618b69652ae3810b8e0bcdb80