SupportingPagesController inherits base class

The SupportingPagesController doesn't need to be a special little
butterfly; it should inherit from DocumentsController like all the rest.
This fixes a bug where unpublishing was not working for supporting
pages.
Rename method for clarity
Merge pull request #1660 from alphagov/unpublishing-supporting-pages-bug

Unpublishing supporting pages bug
Bump govspeak gem

2.0.1 has been yanked!
Merge pull request #1666 from alphagov/bump-govspeak

Bump govspeak gem