Review and revise CiviCRM Code of Conduct

The current CiviCRM Code of Conduct was adopted in 2016 and is fairly boiler plate stuff, and is slanted toward conduct at events. We should review it in conjunction with Eileen's #5 (closed) and make any necessary revisions and improvements. Some past discussion can be found here.

Working document here: https://docs.google.com/document/d/17Ogt364gj2Kl94wr52gqplnSgDmICD5VSI4OYmrlv9U/edit?usp=sharing