add m.constraints and m.constraintsAll

Problem found with apply() of attribute kind In metamodel.scala
412 +    //WHAT TODO ABOUT THIS: ???
413 +scala> Constraints()
414 +<console>:18: error: ambiguous reference to overloaded definition,
415 +both method apply in object Constraints of type (cs:
reqt.Constr[Any]*)reqt.Constraints
416 +and  method apply in trait AttributeKind of type
()reqt.Attribute[Vector[reqt.Constr[Any]]]
417 +match argument types ()
418 +              Constraints()
419 +              ^
420 +    */