New groups section

The Groups section replaces the Policy advisory groups content type. This section needs to be put alphabetically between Detailed guides and Government responses. Please check all the internal and external links. Thanks. These changes have been signed off by Simon Kaplan.
Revert "New groups section"

This reverts commit 1e784da8ca896d0b201d4a32327d4741d47929c6, which
broke the build. I'll speak to @BenClancy to understand what that
change should do.