- close webcam window when receiving webcam stream stopped message from server

...gbluebutton/main/model/users/events/StreamStoppedEvent.as

...g/bigbluebutton/modules/users/services/MessageReceiver.as

...g/bigbluebutton/modules/videoconf/maps/VideoEventMap.mxml

...luebutton/modules/videoconf/maps/VideoEventMapDelegate.as

...bluebutton/modules/videoconf/views/UserGraphicHolder.mxml