Docs update (#389)

* Converted docs to use sphinx extensions ported from OM 3.9 to the sphinx-mdo-lab repo

* Removed the _ext directory from the setup packages

* Fixed sphinx extension names

* Removing docs checkpoints that aren't needed anymore

* Fixing flake and black stuff

* Removed unnecessary case recorders from tests

* Fixed flake8 problems

* Testing changes to see if they work in the docs build

* Still trying to fix the docs formatting

* Even more fixed to the docs

* Changed layout styles and added init files to make the embed-code extension work

* Removed init files because they didn't fix the issue

* Fighting with the custom mesh docs

* Removed commented out code from the tests

* Trying to fix output in the advanced features docs

* Trying to get the docs to play nice

Co-authored-by: lamkina <lamkin@umich.edu>

Author: Andrew Lamkin