- all content actions are now handled
- XEP-0167: the new contents of an offered SDP are added with a single content-add, the
contents sharing a single transport are bundled (XEP-0338)
- XEP-0167: the generated SDP declares the BUNDLE group of its own contents
- XEP-0176: one transport-info IQ per content. ICE data are keyed by content names.
- fix session-level ICE attributes and fingerprint
- use the proper `urn:xmpp:jingle:muji:0` namespace
- replace XEP-0249 invitations with XEP-0482
- the dedicated `META_TYPE_GROUP_CALL` subtype is now used for the confirm action (instead
of `META_TYPE_MUC_INVITATION`)
- handle MUJI invitation: on accept, join the room, start preparing and answer with the
connection method element
- add the `<muji>` element to outgoing Jingle IQs
- propagate the call type (audio/video) in the MUJI invites (the `type` attribute), so the
invited clients set up the proper local stream
- the joining participant initiates the sessions with the other participants, using their
real JIDs, extracted from the presence (the room is set non-anonymous for that)
- only trust the `<muji>` element of a `session-initiate` from a member of the room
- add a `call_group_end` bridge method to clean the MUJI session
- typo fix in `META_TYPE_MUC_INVIRATION` (`R` instead of `T`)
