fix 'report-a-problem' for whitehall

Pull request #311 moved 'report-a-problem'-related code out of 'core.js'
into a separate file. This meant that the code was no longer being included
in `header-footer-only.js`, which is used by Whitehall, thus breaking the
'report-a-problem' widget.
Merge pull request #312 from alphagov/fix-report-a-problem-for-whitehall

fix 'report-a-problem' for whitehall