The close-button should be able to work just like .hide()

In some cases, you might just want to attach the message-panel once, and then just always `.hide()`/`.show()`'ing it, instead of `.detach()`/`.attach()`'ing it whenever you want to get rid of it.

So maybe a option which controls what binding the close-button has, either `.hide()` or `.detach()`. 
`.detach()` should probably be the default, for backwards compatibility...