Fix and refactor column alignment for heading-block

Because this is shared across many templates, I've had to refactor
heading-block. Which fixes this issue across them all.
Topics index/show, topical events, orgs page/index/external,
publications show, consultations show,
attachment full width and world locations.

https://www.pivotaltracker.com/story/show/59109348
Merge pull request #973 from alphagov/fix-refactor-heading-block

Fix and refactor column alignment for heading-block

https://www.pivotaltracker.com/story/show/59109348