Remove .collapsible? check

There is no collapsiblity in hmrc manuals so remove this
Put content list in a list not h2

Before, when content was being displayed inline, these headers were h2s, but now these "headers" are actually links to pages, so remark-up these as a list of links. We can use the classes styled for the other type of manuals for this too.
Add styling for HMRC manuals to accommodate ids

HMRC manuals have section ids, so add (back) in styles for these, and display:table-cell/display:table-row to deal with flexible width of the ids

For mobile, stack the the id/title
Merge pull request #115 from alphagov/style-content-lists

Style content lists