Enum mapping aware service

[greg0ire]

It would be great to have a service that knows which field of which class uses which enum. This could be used by a twig extension that would then retrieve the right label for a value stored in such a field, and translate it (optionally, if translation is enabled), using the class name to build the catalog name by default.

[soullivaneuh]

Ref: #34 (comment)