Fill in features from Minions up to 8

[preaction]

This backend was abandoned for quite some time, and a lot of new Minion features were added. In trying to get this backend working for Minion 7, I just kept banging on it until it worked. This has left it in a marginal state with a lot of the good Minion features not working correctly, like automatic retries.

We should go back and fill in all the features from the current Minion. We can take the Pg backend test, and then work on the MySQL backend so that all the tests pass.

I've started work on this on the fix-features branch. The test is migrated over, now we just need to make all the tests pass.