Refactor webrtc audio management

Attempts to:

1) Successfully play ringtone through speaker instead of earpiece
   when possible.

2) Manage bluetooth headset connectivity as well as possible

3) Eliminate notification sounds while in-call when possible

4) Make sure audio is correctly setup when receiving calls

Fixes #6271
Fixes #6248
Fixes #6238
Fixes #6184
Fixes #6169

// FREEBIE

res/layout/webrtc_call_screen.xml

@@ -176,7 +176,6 @@
                     android:layout_width="match_parent"
                     android:layout_height="wrap_content"
                     android:background="@color/textsecure_primary"
-
                     android:paddingLeft="24dp"
                     android:paddingRight="24dp"
                     android:paddingTop="16dp"