hgroup got removed from the draft spec. replaced all instances with divs for now.
Fix test for markup-based failure

The test was breaking as changing a hgroup to a
div added whitespace before the page heading. The
test was for the presence of the title, not the
spacing around it.
Replace remaining hgroups
Merge pull request #390 from alphagov/remove-hgroups

hgroup got removed from the draft spec. replaced all instances with divs...