Give the ProductFolder back its type restriction. After ZClasses are gone, you...

Give the ProductFolder back its type restriction. After ZClasses are gone, you cannot manage those TTW anymore. Automatic creation as part of the startup process still works.

lib/python/App/Product.py

@@ -59,6 +59,9 @@ class ProductFolder(Folder):
     meta_type = 'Product Management'
     icon = 'p_/ProductFolder_icon'
 
+    all_meta_types=()
+    meta_types=()
+
     # This prevents subobjects from being owned!
     _owner = UnownableOwner