Add a tox job for generating docs

Add a tox job to make it easier for developers to generate their
own docs before submitting a patch.

Change-Id: I9c53ce664b164003fe42ed03d1f850d954bf0971
Update theme for docs

The current developer docs theme used is out of sync with the other
openstack projects. This patch will update the docs to provide a more
consistent look and feel when using developer docs

Change-Id: I97817b8c6d8bef71c4f237be864d1e79dc09098c
Merge "Add a tox job for generating docs"
Merge "Update theme for docs"