Make FeedEx available to all users by default

FeedEx was initially fenced off behind a specific permission
while its usefulness was being tested. Since then, there's been sufficient
uptake of the available features to warrant a wider release.

This change allows anyone with a GOV.UK Signon account to browse
anonymous feedback left on GOV.UK.
Merge pull request #200 from alphagov/make-feedex-available-to-all-signon-users

Make FeedEx available to all users by default