Add "addChangeListener" to ktx-actors

[CreamyCookie]

Thanks for the libraries. @czyzby 👍

Here's a little addition I wrote to make it easier to write ChangeListener to button etc. events, since according to the Vis*Button these are recommended since they don't trigger the event when the button is disabled (contrary to ClickListener).

inline fun Actor.addChangeListener(crossinline changed: (event: ChangeListener.ChangeEvent, actor: Actor) -> Unit) {
    addListener(object : ChangeListener() {
        override fun changed(event: ChangeEvent, actor: Actor) {
            changed(event, actor)
        }
    })
}

Then one can add a listener like this:

addChangeListener { event, actor -> 
    println("ouch.. that hurt. Please don't click me again :(")
}

[czyzby]

It's already there in ktx-actors under onChange/onChangeEvent. See events.kt. Thanks for the suggestion though, don't hesitate to create a pull request next time. 👍