Research nav

[rjkerrison]

Implements the new research sticky navigation parts of #53.

• [x] colours
• [x] hardcoded js variable to generate the links
• [x] scroller on mobile and tablet
• [x] centered on desktop
• [x] hover states and colour highlights

Note that currently because there aren't any pages, I'm hardcoding "school years" to be the "current-page" class.