Build for Python 3.7

Created by: Zaharid

The future is now!

I have no plans for dropping support for 3.6 in the near future until it becomes an issue (for example because it duplicates the CI load).

Regarding the language not a lot of backwards incompatible features were introduced, so I am not planning to break the code for them. Dataclasses is probably the most interesting, but it can be used as a library in 3.6. Could be used to replace the clumsy models in validphys.core, which are a poor man imitation.

New installations are encouraged to use 3.7.