Fix 2-line guide parts

Includes fix for hover styles in guide parts.
Pull out report-a-problem CSS to give whitehall access

Whitehall doesn't make use of core, but we now need the CSS for the
feedback form. This makes it available in both header-footer-only.scss
and application.scss
Remove rems in favour of pixels

We were never really benifiting from using rems as we never changed our
base font-size.

Using rems was causing issues with firefox due to the way it has
implemented minimum font size. In firefox the minimum font-size ensures
no element can have a font-size lower than the specified size. This was
causing the html element to have a font-size bigger than the 10px we
were expecting. This caused some display issues for those users.
Merge pull request #270 from alphagov/remove-rems

Remove rems in favour of pixels
Merge pull request #264 from alphagov/travel-advice-part-fix

Fix 2-line guide parts
Add missing elements to hide on print

User survey and skiplinks should not show.
Merge pull request #269 from alphagov/report-a-problem-css

Pull out report-a-problem CSS to give whitehall access
Merge pull request #271 from alphagov/remove-bars-from-print-css

Add missing elements to hide on print
Merge branch 'master' of github.com:alphagov/static
Merge branch 'master' into callout-killer
Repositioned icon so it's centred with first line. More flexible for varied line lengths and works with single lines
Added min-height to download link so icon is not cut off on single line file titles