Add new deserialization feature that allows lazy error reporting for unhandled types

Currently error is thrown during deserializer construction, if type of any property (implied by a setter, public field, or creator method) involved is unknown (no explicit mapping for abstract classes) or construction of deserializer fails (class has no public constructor etc).
This is often good, since it surfaces problems early.
However, sometimes it would be more useful to only indicate an error if matching property is encountered – it may be ok to have potential problems, but if such property is never encountered there is no need to fail deserialization.

It should be fairly easy to add a feature that allows throwing of such exceptions be deferred until deserializer is needed.