JSON serializer
Add startDate and endDate
Implement from_prop_dict method
Fix __init__ and setter
Move Asset to its own file
Fix list JSON serialization
Implement Serializabe.from_json
Split classes to separate files
Complete model test
Remove debug output
Rename from/to json method
Implement JSON serialization to/from file
Test JSON file serialization
Merge branch 'feature/JSON' into develop