Showing structure should indicate num and heading separately

[longhotsummer]

So it's easier to see when the num is part of the heading (or vice versa)

[longhotsummer]

Our XSL doesn't allow this, because the num and the heading are merged into one heading element, such as

<h2>Chapter 1<br>Founding provisions</h2>

[longhotsummer]

Dup of https://github.com/laws-africa/law-widgets/issues/106