Rewrite insertion of menu items by null and Nyquist modules...

... using the new registration system, and without the fragile hacks making
assumptions about the positions of menus within the menu bar.

src/ModuleManager.h

@@ -38,8 +38,7 @@ typedef enum
    AppInitialized,
    AppQuiting,
    ProjectInitialized,
-   ProjectClosing,
-   MenusRebuilt
+   ProjectClosing
 } ModuleDispatchTypes;
 
 typedef int (*fnModuleDispatch)(ModuleDispatchTypes type);