Gui throws exception when attempting to have a class inherit from an enum

[Wisam Al Abed]

The structuralview throws an exception when there is an attempt to inherit from an enum. This does not break the program nor seem to cause anything strange.

there is a null pointer exception that gets ignored during command execution

To replicate the exception follow these steps:

1. create a new aspect
2. add a new class
3. add a new enum
4. select class
5. tap and hold on enum to attempt to create inheritance relationship

[Matthias Schoettle]

Resolved issue #122: Prevent inheriting from Enums. The call is forwarded, because otherwise code has to be duplicated in EnumViewHandler to enable edit mode. Therefore, an additional check is necessary to prevent inheritance.

→ <<cset 11da3e630967>>