Compare class sels

Summary

This MR introduces the following changes

• Instead of comparing only the class label values to avoid using the same class definition, the class label values, operators and variables are compared. In the current implementation it would not be possible to use classes which are e.g. defined by using the operators "!=" and "==" if the label values of both classes are the same.

Conformity

• Changelog entry
• Documentation
• Development guidelines
• Style guides