Enable Event capturing

[jamowei]

It is now possible to listen on events in capture-phase (suffixed by Captured):

render {
    div {
        clicksCaptured handledBy store.save
    }
}

For this we added new options to the subscribe() function which gives you a Listener for your event:

subscribe<Event>(name: String, capture: Boolean, init: Event.() -> Unit)

Using the init-lambda you can make settings to the captured event that have to be applied immediately.

We also fixed a bug when using stopPropagation() on a Listener which sometime did not work as expected.

fixes #552

[ghost]

Looks very good!

The tests are running and the code looks clean.