Switch theme, fix navigation

This PR switches the theme to the Bootstrap-based one by Surya Kasturi, and fixes the currently extremely broken navigation structure of the site.

Run
```
git submodule init
git submodule update
```
to get the theme after clone/pull.

Also, Trac->Github and remove some outdated information.

We can move the scipy-sphinx-theme repository under scipy organization. I think we want to use it for the docs, too etc. whatever sites we have floating around.