Incompatible with Py3.8 due to type hints

[emirkmo]

See: https://bugs.python.org/issue45117

Problem: type annotations like dict can't be subscripted before py 3.9, even with from __future__ import annotations.

Solutions:

• Move from python native types to the typing library types like typing.Dict
• Require python 3.9 (also means flows project needs to be upgraded to python 3.9).
• add compatibility for 3.8 using typing library somehow without rewriting the entire codebase.

I prefer moving to py 3.9, will investigate that for flows. Also makes it easier to begin type hinting flows.