Support event delegation to subscribeTo()

[maberer]

Add support for delegation of events when using subscribeTo()

this.subscribeTo(DOMElement|Widget, eventName, nameOfHandlerFunction|Function)

Without event delegation/bubbling of events, adding listeners could become costly...

This is even worse, since client side rendering requires you to add listeners via JavaScript (there is no way to use the more performant declarative events in this case)