* Changes initialization of videoSIPGW.

* Adds some errors returned on creating videoSIPGW session.

* Fixes sending videoSIPGW session STATE_CHANGED event.

* Fixes sending jibriIQ, no result status is received.

* Adds VIDEO_SIP_GW_SESSION_STATE_CHANGED to JitsiConferenceEvents.

* Fixing comments.

* Adds video sip gw handling.

Parsing presence and availability of the service. Adding possibility to start/stop a video sip gw session.

* Fix comments.

* Adds more jsdoc about create session and renames import to use the filename is imports.