Support schema model class being an interface or abstract class

[lindyhopchris]

We need to add support for the $model property of the schema being an interface or abstract class. Both the schema container and the resource container will need to be updated. We can work this out using PHP's class_implements and class_parents.

Basically the logic is to look for a direct match first, as this is quickest. If nothing matches, we can then see if there is a schema for any of the parent classes, and then if there is a schema for any of the class interfaces. When working this out, if we find a match it needs to be cached as a direct match so we don't run the lookup logic twice.