cubicweb-jsonschema #17088618 remove IJSONSchema adapters [done]

Currently the respective role of IJSONSchema adapters is not very clear when considering aside of mappers. It seems that mappers should be responsible for producing JSON Schema (dict) at various levels (entity, collection, relation) and handle serialization/deserialization at the same level. In this respect, the usefulness of "adapters" is not obvious so we should either find a use case for them or drop them. Maybe they could be used as entry point between mappers and db-operations (for instance manipulation of deserialized values before insertion in the db)?

done in0.5.0
load left0.000
closed by#b6550ea53e9d Remove IJSONSchema adapter