fix US orgs
Merge pull request #185 from github/org-cleanup

Fix US orgs
.homepage-image: specify box-sizing so that the box is what we expect it to be.
Fix footer links with low resolutions.

Hide them like it was done before, but cover all low resolutions now.
Fix selector name.
Remove unused selectors.
No need to use only screen in media queries.
style.css: remove background-size from homepage-image for low resolutions.
icons.css: use the shorthand property for font.
Fix :not selector.