Submitting responses without assignees shouldn't be possible

CORE-615
Yes, it's named after old-style jQuery .bind (which is now merged with .delegate as .on), and can listen to every change on an object (```.bind("change", function(ev, how, attr, newval, oldval) {...})```" or individual properties (```.bind("foo", function(ev, newval, oldval) {...}```).

You can read more about it here: http://canjs.com/docs/can.Map.prototype.bind.html