unique_together integration in CW (alf+syt) * added in-DB representation of the constraint with a new entity type (CWUniqueTogetherConstraint) * the schema is now migrated on a sync_schema_props_perms(EType) call in the migration script * removed the migration commands provided in the first implementation

if repo.system_source.dbdriver == 'postgres':
    sql('ALTER TABLE appears ADD COLUMN weight float')
    sql('UPDATE appears SET weight=1.0 ')