Enhancement: Explore CQRS + ES libraries / patterns

[seangwright]

Here are some .NET CQRS + ES libraries I found in a quick search.

https://github.com/eventflow/EventFlow
https://github.com/Elders/Cronus
https://github.com/lucabriguglia/Kledex

Even if we don't adopt any, it might be worth looking at the patterns in each to see how they could fit into this app.