sqlalchemy: uncommenting VARBINARY for PostgreSQL
sqlalchemy: uncommenting VARBINARY for PostgreSQL

* Uncomments VARBINARY for PostgreSQL and resolves a name binding
  conflict. (closes #3066)

* PEP8/257 code style improvements.

Signed-off-by: Leonardo Rossi <5460ec99b71a72e7693c4088b5c2585e76e1c857@cern.ch>
Reviewed-by: Jiri Kuncar <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>

tiborsimko/invenio,tiborsimko/invenio,inveniosoftware/invenio,inveniosoftware/invenio