Use Python data classes

[expobrain]

Generate Python 3 code with data classes using the backport for Python 3.6 support and built-ins for Python 3.7+.

Question is if two generators should be written, one for 3.6 and one for 3.7+, or only one with polyfills.

[expobrain]

Explored the possibility of using dataclasses and for this specific project they are not fit, they are useful if the constructor is called with the proper arguments and keywords but in this case we pass the dictionary of values to the constructor instead.