A plugin that makes shortcuts, in a Shortcuts menu, to other plugins.

This is a prototype that I'm posting for comment.  It works but it could be improved.  I would be glad to start a community project.

A future version might:
- let you enter parameters for the target plugin (make a "preset")
- let you enter some of the parameters of the target at shortcut time
- let you put the shortcut anywhere in the GIMP menus
- be more user-friendly e.g. replacing existing shortcuts
- disallow creating certain shortcuts that won't work (e.g. whose options don't default sensibly.)
- let you create a keyboard shortcut to the shortcut at the same time

Even more in the future: let you script a sequence of calls to other plugins and even GIMP menu items.  Known as a visual script editor or a macro editor.  Would not require knowledge of a programming language.

