Add code to show a message when a conference merge fails.

Right now the plumbing only exists for VoLTE conference calls
and GSM/CDMA calls behave as they did before. While making
this change, it made a lot of sense to rename CdmaDisplayInfo
to PhoneDisplayMessage.

Bug: 18080792
Change-Id: If8c8cf9a234371bdb2798c9d1e80d56b3aaf84f8
5 files changed