CLC-3921 Support updates of events 

https://jira.ets.berkeley.edu/jira/browse/CLC-3921

Supports updates to class events, and does not squash attendees' responses (yes, no, maybe). 
No. response will be from either the update or the insert method. If the update method does not produce a response, then the insert method is called. If insert fails to return a response then there's an error state that should be logged. I'll add that error handling.