Move various data-storage things to DB

[mrphlip]

The reasons for using a JSON datafile over a proper DB is getting less and less relevant as more stuff keeps getting stuffed into there, and the data structures keep getting more complicated... and since we actually have a DB to store things into, it probably makes sense to start storing things in there instead.

It doesn't need to be done all in one hit, but it would be good to start moving things out of the JSON and into the DB, make some proper DB structures to store the game stats, etc.

[andreasots]

I have a local branch where the static responses, explanations and spam rules are fetched from the history table. I added concurrent modification detection as well but it needs a bit more polish.