Allow class names to include "Configuration"

[angelikamentz]

Right now, when a class name contains the word "Configuration" a RuntimeException is thrown on the configuration being null. We want to fix this bug.

[mauricioaniche]

Great! I don't think we should make it work, but more like return a nice message to the teacher, like, "hey, Configuration is reserved, you can't use it".

(We should open another issue to rename this class. "Rubric" would be much better!)