Refactor `session.edn` -> use only as a data file to seed new events

[joyheron]

Currently we have session.edn which we use to start our current session, but we have reached the point where we can change a few more things:

1. Since the session state is saved to a database, we no longer really need to save-seeds! when we stop the component.
2. We could refactor this to be something more like seeds.edn, which would only save the initial structure of the event before we load it into the database. I'd also like this to be a list of events, not a single event, since we will have a list of events to create. (It would also probably be good to modify Events in data.clj so that we can retrieve all of the events)