Add support for transfering support session to another workgroup, queue, agent or user

When an agent is having a chat as part of a support session the agent should be able to ask the workgroup service to transfer the existing support session to:
1) some agent of a workgroup. The workgroup service will decide the best queue based on the initial request
2) some agent of a queue. The workgroup service will decide the best agent of the queue (ignoring the inviter)
3) a given user that is acting as an agent. The agent will receive the offer that could be accepted or rejected
4) a given user that is not an agent. The user will receive a standard MUC invitation.

In any case, the workgroup service will kick the inviter from the room once the invitee has joined the room.