Events registered from menu windows are executed multiple times

[NSSure]

Any windows that are open from the main menu of the editor and register events when open are having those events registered multiple times.

Steps to reproduce the behavior:

1. Go to "File"
2. Click on "Save project"
3. Dismiss the window
4. Click on "Save project" again
5. Click "Save" in the window
6. The project file be saved twice.

This happens to "Save project", "Export", etc.

Need to add a key to track the registered events or create a method for removing registered events.

[unsettledgames]

Fixed in #87