Add verify dialog for some more destructive actions

[nstrayer]

With node deletion it's very easy to delete large parts of your app. While the back button will save you it won't if you leave the editor. For things like this it may be best to give a small prompt making sure the user want's to do the action.

Same dialog component could also be reused for cases like dragging the last item out of a container asking you if you want to delete the now empty container

[nstrayer]

The foundation to doing this is now in place as of #213