Use some new Python3 types

[QuLogic]

PR Summary

This is a PoC of using some new Python 3 types: enum.Enum in a couple places, and replace cbook.Bunch by types.SimpleNamespace. This will fail CI right now.

PR Checklist

• Has Pytest style unit tests
• Code is PEP 8 compliant
• [N/A] New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• [N/A] Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way

[jkseppan]

As illustrated here, types.SimpleNamespace is a lot more characters to type than Bunch, and the pep8 line length limit is quite small. Just a thought: how about from types import SimpleNamespace as Bunch?

[QuLogic]

I don't see the need for a shortcut like that. There are other ways to wrap it, such as the one I just pushed.

[QuLogic]

Rebased due to conflicts.