GridBag in Navigation Panel should show items in order

[KeyWorksRW]

If cells are added to a wxGridBagSizer out of order (e.g., adding row 0 cells when there is already a row 1), the items in the navigation display will be out of order until the project is saved and reloaded.

Ideally, we should recreate the gridbag navigational display whenever a cell is added, or it's row or column is changed. If we can't do this automatically, then the context menu should include an option to reorder the items.