Enable HOLD capability for IMS-based CDMA connections.

+ Refactored method for checking whether a call is based on an IMS
connection into the parent TelephonyConnection class.
+ Changed CdmaConnection/GsmConnection to obtain a populated
call capabilities from their TelephonyConnection super class when
building call capabilities.
+ Add IMS-scenario handling for HOLD when building call capabilities.

Bug: 17913504
Change-Id: I03316a0bea509395fe9a0f0688047f96c72db87e
3 files changed