[GREENFOOT-172] Possible to create a class with a blank name

If you hit edit, then new class, then enter very quickly, a new class is created with a blank name. I believe this is because it's before the frame has fully initialised. Would it be better to set the OK button as inactive by default until something has been typed in? This should solve the problem and also seems nicer than being able to press the button when nothing has been typed in the first place.

Issue metadata

Issue type: Bug
Priority: Medium
Fix versions: 1.4.6