This tries to toggle the next item when clicking on an <h2>
in the sidebar, however we want to first check the next item is
an <ul> element, so that we are collapsing or showing a list,
instead of something like an <h2> which currently happens with
the "#guides" element.
This makes the /help/ sidebar more discoverable at windows less
than 1000px in width because it makes it stick out a bit when it
is closed with the hamburger menu at the top.
Fixes: #6038.
This redesigns the /help/ page sets to be a single page app that uses
history.pushState to work the same as the old app.
The big new feature is that now we have the index in a nicely designed
left sidebar.
