404 and 500 error page designs

Please check over the copy of these pages

500: will "refreshing the page" be a problem?  (Note to self: "refresh THIS page")
Could that be a link back to the previous page?

How to embed footer id="app-footer" onto each error message page?
Error message pages

Altered styles and messaging
Fixed URLs in error page links.

Conflicts:

	app/helpers/homepage_links_helper.rb