Don't use GRUU for conference subscriptions and referrals

Ignore-this: 6dc2aba919c0ebfd38b391d595b5b7da

darcs-hash:20121004110541-56b4d-91c2b52a23d08927d7b70a8d59293645802a38d9
Moved identity attributes from MSRPStreamBase to ChatStream

Ignore-this: a4ba1acc8655c115704e78454134b2b7

darcs-hash:20121011115753-56b4d-e6d6a8a7c31f3416524d652fb82e2282c4d24387