clean up "Add" menubar categoes on the 3d object side via the following:

SceneObject now defaults to a category of "misc"
getCategoryOfClass now checks parent classes for what categories they hold so that variants can inherit
categories are in one of a few rough groups and subgroups depending on actual mapper needs/usages

Engine/source/T3D/notesObject.h

@@ -67,6 +67,7 @@ public:
    // Declare this object as a ConsoleObject so that we can
    // instantiate it into the world and network it
    DECLARE_CONOBJECT(NotesObject);
+   DECLARE_CATEGORY("Markers");
 
    //--------------------------------------------------------------------------
    // Object Editing