Adding indentation on lists in content

As per https://www.pivotaltracker.com/story/show/67910018, I've added
indentation to lists.
Merge pull request #104 from alphagov/change-list-indentation

Adding indentation on lists in content
Merge commit '51c3629c3826803ea2d7e9bf7f1c119e4ddcaef5' into HEAD