Update theme for sphinx 2.0 compliance

[jputrino]

Version

1.0.7

Description

Sphinx has made a lot of updates in advance of the 2.0 release, which will fully support python3 (among other things). We need to review the changes, especially the deprecations, and update this theme accordingly.

For example:
Running sphinx 1.8 with v1.0.7-beta produces this error:
/usr/lib/python2.7/site-packages/sphinx/builders/html.py:138: RemovedInSphinx20Warning: builder.css_files is deprecated. Please use app.add_stylesheet() instead.

This means that we need to update how we call css files from the theme layout.
(We should change this so that we're using central resources from the clouddocs project and move the files out of this repo.)

[jputrino]

We should also review this page and incorporate any changes/updates as appropriate:
https://www.sphinx-doc.org/en/master/templating.html