linting / type definitions

[Jonathan-Dobson]

Origin of this issue

          @Jonathan-Dobson if you put the linting / type checking commands you use into a separate issue that would be the best way for us to go about getting them resolved.  That way we can reproduce them and fix them. (You are also welcome to send PRs yourself if you feel comfortable doing so).

Originally posted by @awni in #973 (comment)

Does the community have any preferences about type definitions?

Are there any preferences, recommendations, or general guidelines that should be adhered to aside from the contributing readme, as we build in type definitions?

High priority files that need type definitions added first. List here.