Regenerate the Bootstrap stylesheet.

This is mostly to fix the .btn-primary rendering. I have also incorporated
the hover colour into the Bootstrap stylesheet, so this is removed from
the Site.css stylesheet.

I will document the full set of overrides in #37 so we can refer back to
it if we need to do this again.
Fix text shadow on navbar text.

Change the text shadow from green to a mid gray (#666666). This is
subtle enough to not be obvious, but makes the text much more defined
and easy to read.