Make SASS code tighter
Add a partial for the "what went wrong" form to 40X pages
Provide a simpler 40X page style

Removed the search and exploration options for the time being as
discussed with @AmyWhitney. Keeping the error page as simple as
possible and adding the report a problem form.
Provide IE fixes for labels

They need to be full width to trigger the margins we set otherwise the
labels and inputs are set tight together.
Use a simpler heading for404 pages
Add the JS referrer field appender to the 40X pages
Merge pull request #232 from alphagov/error-page-style-and-copy

Update styling on 40X pages