Solution serialization

Summary

Solutions should be serializable.

Possible fixes

Solution and depending classes should implement to_json_data method that generates a CoBRA conformant dict which can be turned to json.

Classes that will need changes:

• Solution (needs to serialize header data and dependent classes)
• Assembly / Robot (needs to know module order)
• Module database (needs to know its CoBRA name)
• Trajectory
• Cost function