Remove dependency on can-define

[DesignByOnyx]

In order to support two decorator syntaxes, we need to determine whether or not a DefineMap constructor or plain object is being passed:

@singleton
const MyType = DefineMap.extend({});

@singleton( options )
const MyType = DefineMap.extend({});

Right now, we check whether or not the decorator arguments pass this test:

function singleton(Obj) {
  if(Obj.prototype instanceof DefineMap) ...
  else ...
}

It should be fairly trivial to change this into something more generic - something which uses can-reflect'sisPlainObject() or possibly isConstructorLike(). My vote is for the latter.

Furthermore, there's code in here which defines a List property on the constructor if one is not yet defined. This code can go away whenever this issue is resolved:
canjs/can-connect#446