Move IE8 shims and fixes so they load after styles

* For respond.js to work correctly, it must load after the CSS has
loaded (it uses media queries in the CSS files to determine styles to
display). Also, from the docs, “Reference the respond.min.js script
(1kb min/gzipped) after all of your CSS (the earlier it runs, the
greater chance IE users will not see a flash of un-media'd content)”
Merge pull request #27 from alphagov/ie8-respond-fix

Move IE8 shims and fixes so they load after styles