"Add" enable video call setting to call settings.

+ Add in the sense that it is implemented, although it is always
removed for now. Further work needs to be done to condition the
display of this setting on VoLTE support.
+ Make PhoneInterfaceManager's storage of shared preferences more
generic. Add a key to store whether video calling is enabled.
+ Add "Turn on video calling" option to call settings, and update
the share preference when changed.

Bug: 16014284
Change-Id: Id6ac1f55b3933c33f8653622ae0fea961d1644eb
3 files changed