Add ExtendedType to generate user-friendly exceptions for internally used values

We have some internal values that could be used in a DB query and cause exceptions. In that case all the information user get is a confusing message like this: "Haven't found suitable ExtendedType for class 'org.apache.cayenne.access.flush.IdGenerationMarker'". See CAY-2726 for example.

We should add some special ExtendedType to handle those types and generate user-friendly exceptions.