Bump to 2.3.0
Use full namespace for association class
Fix translators

Makes translators use @form.create_association instead of using the
hard-coded class name
Remove all support for raw/unmapped data

In our project, we handle this outside the form layer, and as mentioned
in the README, it was of unknown value since the mapping to attributes
makes losing existing data unlikely (previously we were rewriting the
RDF in full, so the form needed to be aware of this data)
Bump to 2.4.0