Equility operator for SingleSet, Modules, Bodies, Joints, ...

Summary

Introduce the __eq__ operator for

• SingleSet
• ModuleBase
• Body
• Joint
• Connector
• Geomtry
• ModuleAssembly

What's is needed for?

Easy unittests for (de)serializing!

Roadmap

A proper implementation of __eq__ needs an accorindg __hash__ which can, for the general case, either be achieved using the elements unique ID or a sum of hashes for contained objects.

/cc @JonathanKuelz