Fixed issues with screenshare.

[barankyle]

Summary

Backend was not handling closeProducer and closeConsumer messages. WebRTCFunctions.ts was not saving producer objects in MediaSoupMediaProducersConsumersObjectsState. Close messages now attempt to close the object on in the instanceserver.

Fixed a bug where screenshare consumers that are closed were still showing as userScreens.

References

closes #insert number here

QA Steps