Use a BroadcastReceiver for Dialpad behavior upon call hangup.

The case handled here is when a user is in the Dialer app while there is
a call in progress and then the call ends, the Dialpad should revert to
its "normal" mode, i.e. digits. The previous approach, using
PhoneStateListener, was safe for single SIM phones, but no longer works
on Multi-SIM phones because a PhoneStateListener only listens to state
changes from a single subscription (e.g. SIM). A more robust way of
knowing when a call hass ended is to receive a
TelephonyManager.ACTION_PHONE_STATE_CHANGED broadcast.

Bug: 18269410
Change-Id: I9b0578d4281bc75d0f804dc695f4bd1a9c02f2cd