Improve speed when an account has lots of events

[udl]

Is your feature request related to a problem? Please describe.
The amount of events that we've generated in our compose-us account already leads to reduced startup speed for todastic. We should take care of that.

Describe the solution you'd like
It would be good to introduce a snapshot feature and on reload deliver the snapshot as starting point instead of all events. Snapshot would also need to know, at which point in the event stream it currently is.