Bump Mypy

[Jepson2k]

Which files would be affected?
Mypy static checking has grown a lot and provides more useful analysis in later versions, but with the introduction of PEP 484 and the banning-ish of implicit optionals there are a lot of type hints that will need to be added to many files. Mypy recommends a program that auto converts the code base so it shouldn't be hard to do but it'll affect many files.

Does the proposed maintenance include non-doc string functional changes to the Python code?
Yes

Are you interested in implementing it yourself?
Yes

[whyitfor]

This should be tackled in a PR that only changes this and nothing else, to isolate these changes