[repo threads] Add several safety when looking for a callable name. We lookup __name__ attribute, then func_name attribute. object repr is a last fallback

[facets] support for `no_relation` on RelationFacet e.g. to filter en entities *without* a given relation as well as with a particular relation. Proposed or not by default according to relation cardinality. Also, try to guess i18nable properly from the schema by default.