Attach home background image to #jacket

This will make it so the home background image can be easily overridden
using the multiple thumbnails background image. Remove unused
backgrounds while we’re at it.
Make unbound/rebound border box size

The needs to move the Spine framework. And the prospect of making all
things use the border-box model continues to have its allure.
Merge pull request #111 from washingtonstateuniversity/home-background

Fix background image attachment on homepage in bookmark style