Can't disable on cron via the UI

I've added a MR that:

1. Defines a config schema for the settings, so that settings get proper exported as the correct types etc.
2. Saves the autoban_cron setting when the form is saved.
3. Uses the autoban_cron setting correctly when running cron.

@Steven, thanks, comitted

Automatically closed - issue fixed for 2 weeks with no activity.