Explicitly Bind @class For Handlers

To create a delegate, we need to cast the source to the exact class
type, and have a reference to the method of the class that will be
called. I facilitated that by adding a "forHandler: 'SomeHandler'"
property to @class. This lets us get direct references to the class and
method. It's the easiest approach, I don't know if it's the correct one.
Further up, further in!