Add the 'Report a problem' link using JS

This means that if you have JavaScript disabled, the link never displays
on the page. This changes the current functionality, which is that the
link is still displayed when JS is disabled, but reloads the page.
Merge pull request #375 from alphagov/hide-report-a-problem-link-when-js-off

Hide the 'Report a problem' link when JS is off