[console] Auto-complete container is not removed from DOM when dialog closes

The add-node/add-property dialogs both use a Wicket auto-complete widget. This widget should be removed from the DOM when either of these dialogs is closed, but it is not.

This means that, for example, opening&closing the add-node dialog 20 times will result in 40 hidden auto-complete widgets in the DOM that will stay until a refresh/logout occurs.