[Liverpool] Fix container responsive widths
[Liverpool] Don't use the header tag

The liverpool stylesheets have some very general styles for header
elements that apply to all header elements on the site. The simplest fix
seems to be simply avoiding using headers.
[Liverpool] Wrap all styles in body.liverpool selector

This makes all selectors more specific, therefore more likely to do what
we want.
[Liverpool] Fix navigation position on the mappage

Without this the nav becomes fixed in place and doesn't look correct.