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
sync_schema_props_perms('state_of')
sync_schema_props_perms('transition_of')
for etype in ('State', 'BaseTransition', 'Transition', 'WorkflowTransition'):
sync_schema_props_perms((etype, 'name', 'String'))