Refactor sections into list of links

WHYYYYY:

- Future plans for this are that clicking one of these titles will use JS to load in the article. Better described in this ticket: https://trello.com/c/63tlc9rE/72-urls-for-hmrc-manuals.
- Given this, it is better to have a <ol> of <a> rather than a groups of sections that contain some links.
Fix up styling after HTML refactor

- Style control links so they tuck in on the left for mobile and don't mess with the (optional) list title on wide+tablet screen widths
- Styling for sections as a list of links rather than a stack of sections
- Move arrows onto a negative margin
- Override default list and link styles
Update JavaScript

- Add controls inside a div
- Work with HTML refactor
- Update tests to work with new HTML
Make disabled style work again
Replace section with div, add class to ol

Add class to ol so that the js doesn't add Open all Close all links to any ol that it contains
Replace section with div as the section won't always have a title or a body, depending on what comes in from HMRC
Merge pull request #19 from alphagov/refactor-link-lists

Refactor sections into link lists