Turn ro.py objects into Python dataclasses

[jmkd3v]

The Python 3.7 feature "Dataclasses" could be very useful for ro.py. Our objects, like User, should be immutable as the only way to return new information is generating a new object entirely.
https://docs.python.org/3.9/library/dataclasses.html

[jmkd3v]

Closed until v2.1.x.