[GREENFOOT-179] classes subclassing Actor or World class via a userlib not recognised as World and Actor

If you have an Actor or World subclass which became a subclass of those classes via subclassing a class in a userlib (i.e. the uselib class subclasses World or Actor), the class will appear in the 'Other Classes' section of the class list in Greenfoot. Creating a new instance of the World subclass does initiate a World, however you cannot add the subclasses of the Actor with the mouse (like the shift+click interface).

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Issue metadata

• Issue type: Bug
• Priority: Medium
• Fix versions: 3.0.0