Integrations that want to work with conditions can now do so by adding

one or more ConditionsFields to their configuration form. These will

automatically be set up with the appropriate Local Site, ensuring that

any querysets contained within are LocalSite-aware. The integration can

then match against those conditions when iterating through the list of

enabled configurations through a new config.match_conditions() method.
This all makes it very easy for an integration to allow for

customization based on conditions, without being locked into a

pre-determined set of condition choices or use cases.

Unit tests passed.
Manually tested all this with a new Slack integration.