This class creates the File pulldown menu.
Create the menu.
Clear the model and filename, but ask to save the JSON document, if unsaved changes have occured.
Open a file and load it into the editor. Ask to save the JSON document first, if unsaved changes have occured.
Quit the editor, after asking to save any unsaved changes first.
Revert the current JSON document in the editor to the saved version.
Save the current JSON document.
Save the current JSON document under the given filename.
[Validate]