GabbleMediaChannel: implement local hold/unhold functionality
GabbleMediaChannel: implement local hold/unhold functionality

This version hasn't been tested with multiple streams, and doesn't actually do
any XMPP signalling (our implemented version of Jingle is too old).

20080327194651-53eee-d94888f9bc6bd575c7d7aa4639bcf05fccbe8d20.gz

mlundblad/telepathy-gabble,community-ssu/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,community-ssu/telepathy-gabble,jku/telepathy-gabble,community-ssu/telepathy-gabble,Ziemin/telepathy-gabble,community-ssu/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,jku/telepathy-gabble,jku/telepathy-gabble,Ziemin/telepathy-gabble