Reuse the edit menu.

Create a copy of each selected dictionary, or merge them into a new one.

Default to the configuration directory, instead of the current directory.

No editing or "saving as" until a dictionary is loaded.

Note: this does not strictly prevent trying to edit a loading
dictionary because the code does not filter the list of selected
dictionaries before attempting to do so. But this is use case will
result in the interface freezing until all selected dictionaries have
finished loading (and then the editor will show up).

Default to the configuration folder, and then remember and re-use
on subsequent invocations.