Merge develop branch in master.
Remove RFC 3261 18.1.2 sanity check (sent-by host mismatch in Via header).
This allows JsSIP to interop with non very compliant RFC 3261 servers.
RTCSession: Send AKC+BYE after receipt of a 2XX with wrong SDP (fix #234). Credits to @mEkblom.
Improve session status (related to #234).