Add a database

[wridgers]

I suggest we just use a postgres docker image.

We should also provide some mechanism for automatic migrations. On start, the bot should do something like this:

• create migrations table if it doesn't exist
• iterate over files in migrations/, run them if there is no row in migrations table

[nullren]

• what exactly are the migrations?
• if migrations don't exist in psql, then why would we look in the folder?
• why not just use the folder?