Convert GsmConference into more generic TelephonyConference.

+ Retype Conference and Controller to handle TelephonyConnections
rather than GsmConferences.
+ Rename classes.
+ Add connections to TelephonyConference if IMS is supported, and
the original connections are IMS connections (even if the
TelephonyConnections are CdmaConnections).
+ I haven't been able to test these VOLTE changes on CDMA because
of network instability. For existing GSM calls, TelephonyConference,
and TelephonyConferenceController should not cause any changes. We
need to verify that these work properly with IMS on CDMA phones.

Bug: 18062269
Change-Id: I2d7f717b2560b69c6579072dcdd5bec583062b38
3 files changed