[Nsi-wg] updated description of connection service messages

I added to the description of connection service messages, based on discussion last week. I think this is better, but I am sure there are lots of questions and things that need to be added and improved. It has a number of issues that might be good to get identified as concepts we agree on or need to discuss more. Perhaps someone could make a stab at that so our conversations can be productive. I hope this is useful - please make suggestions, or modify. John