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.
Allow gemfury change
Try to capture more about where the problem is

This will be character rather than line, but it’s a start.
Reformat, fix markup
Fix failing test
Rename resource and redirect appropriately

Discussed with @BenClancy.
Merge pull request #182 from alphagov/feature/groups

Style guide change requested by content designers