Make new session note into a snippet

[jennapederson]

Session length varies based on the specific event. The session note should be a snippet, if possible, to make it configurable rather than a require a code deploy every time. There may be cases where we don't need to show a snippet, so an empty value wouldn't display anything.

[willbuck]

I can take this one on!

[experimatt]

I think this could be as simple as adding a field to the Event model/table: max_session_length.

We would of course still need to ensure that the timeslots we (manually?) create for the event honor this value though.