Preserve sphinx theme set in project configuration

[drdavella]

Currently the generated schema documentation does not conform to the theme that is set in the project's docs/conf.py. This is because we use the sphinx bootstrap stylesheets to generate schema documentation, so they get pulled in regardless of whether the project is using sphinx-bootstrap-theme or not.

I'm not sure whether this will be possible and/or how much effort it is worth.

[drdavella]

This is just a shot in the dark, but it's possible that we could fix this by calling super() in this section of the template: https://github.com/spacetelescope/sphinx-asdf/blob/04f56ef65acaf38ff6202ce3de7d25c9af93456a/sphinx_asdf/templates/schema.html#L3-L4

[braingram]

I believe this was fixed in: #88