Peter Wu authored Aug 26, 2018 and Oliver Sander committed Aug 26, 2018

Large specifications with many (nested) sections are painful to navigate
through when the TOC is expanded by default. Introduce four new options,
"Expand/Collapse whole section" is based on Kate's document view while
"Expand/Collapse all" was added to handle the top-level sections.

As for other viewers, PDF.js uses shift-click to handle the former while
using double-click on a the TOC icon to handle the latter. That is not
very obvious, so extending the context menu seems the next best option.

BUG: 216870

Differential Revision: https://phabricator.kde.org/D14904