Allow a Sphinx conf file to be configured based on the builder.

This gives greater flexibility in configuring the generated output
for each builder type. At this point the output is the same as it was
for the single conf file case.
Refs #9761
Turn off the fixed navigation bar.

It now only appears when you are looking at the top of the page. This has
the side effect that when the bar itself increases in height then the rest
of the page content is pushed down as expected.
Refs #9761
Remove h1 top margin

The navbar already has a 20px margin-bottom so we don't need to add to
that.
Refs #9761
Add conf-builder files as dependencies of the relevant targets.

Refs #9761
Remove all links from the navigation bar.

It's not possible to the contact to become a mailto: link as they don't
work in QtAssistant.
Refs #9761
Remove the search box for the embedded qthelp html.

Defines a navbar html template that removes the search box when in
embedded mode.
Refs #9761
Add a dependency for the docs-* targets on the runner script.

Refs #9761
Merge remote-tracking branch 'origin/feature/9761_remove_navbar_links_offline_help'