onRemoved callback

[Johan Gorter]

It is sometimes necessary to do some cleanup work after DOM nodes are removed from the DOM again. This is needed for example if a component added a resize event listener to the window and you want to unregister it when the node is removed from the DOM. We want to make this possible using a callback. This callback will be called eventually but not directly when the node is removed, probably during idle time.

This is one of our ideas for maquette 3