Play the ringtone for incoming calls in Dialer

+ Initial CL to make the Dialer play a ringtone for incoming calls.
- Not included in this CL:
  - Playing call waiting tone
  - Silencing ringer when volume key is pressed (power button works
    properly)
  - Bug fix for ringtone not playing when lockscreen is set
  - Bug fix for contact look up taking too long - when do we play the
    default ringtone
Change-Id: Ie8bd042b9ec142c78cb4d2de66475c96a18b8273