This commit makes the mahara them inherit from sphinx:classic instead of
basicstrap. The basicstrap dependencies are also removed.

- theme.conf updated to:
  - change parent to `classic`
  - mahara.css is commented out as it prevents the sidebar from being rendered
    in the new theme. Rather than being commented out mahara.css should be made
    compatible with the new theme.
- layout.html has been removed as that has dependencies on basicstrap. This
  may need to be changed if layout changes are required. Hopefully any changes
  can be limited to css and theme config.