connection: implement ContactCapabilities interface
Killed several build warnings
call-stream: remove useless code and use TpBase class vfuncs

I'm not quite sure what half of this code was even doing here.
tests: stop calling g_type_init()
call memset with the correct third argument
stop calling tp_handle_unref()
stop setting values to unused variables
stop calling g_strcasecmp()
text-channel: use TpCMMessage
call-stream: remove unimplemented function declaration
call-stream: add missing _init()
call-content: remove unused useless functions
Start moving RingCallChannel to depend on RingBaseCallChannel
Implement HOLD interface in RingCallChannel
Add skeletons for TpBaseCallChannel's method implementations
Add ring_call_channel_get_call_service
Use RingBaseCallChannel as prerequisite for RingMemberChannel interface
TpBaseCallChannel's hangup is already implemented in RingBaseCallChannel
call-member: comment out extraneous line

This should have been commented out in an earlier cleanup commit.
call-channel: add {de,}queue_request from media-channel

We can't use RingMediaChannel's methods as they are for a different type.