Assets for HAS module themes, with backgrounds

This splits HAS into five themes, which share a common CSS file (has-styles.scss) but also have custom files which pull in different background images (and, eventually, different header graphics). This is most of [#53912853]

https://www.pivotaltracker.com/story/show/53912853
Themes haven't had footers for a few revisions
Migration to create five HAS themes

Just a quick way to create five themes without using a form [#53912853]

https://www.pivotaltracker.com/story/show/53912853