72c6b83866
Implement the EditWeight undo command. Since there is common code (storage of the old weight), this creates a common base class for RemoveWeight and EditWeight. The model calls directly into the undo command, which is somewhat unfortunate as it feels like a layering violation. It's the easy thing to do for now. Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>