[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.

[R] use dbhelper.binary_value to process passwords and other Bytes fields (instead of dbapi_module.Binary or hardcoding buffer()). This requires (esp. in serverctl) version 1.3.1 of logilab.database. Dependencies updated.