[entity] Entity.related(): add a targettypes argument (closes #2957313)
This allows to restrict the entity types returned by the method
(passed to cw_related_rql).
When such an argument is given, no caching happens.
drop_relation_definition('CWSourceSchemaConfig', 'cw_schema', 'CWAttribute')
sync_schema_props_perms('cw_schema')