Make the feed private, and add private datasets too
Merge branch 'master' into 529-rss-admins
Add tests for the dataset rss
Remove list_changes requires
Make the dataset RSS public and add tests

- Removed the admin-only requirement for the RSS.
- Admins can see private and public datasets in the RSS.
- Advertise the RSS feed in the datasets page.
- Test ALL THE THINGS.
Merge pull request #536 from openspending/529-rss-admins

Show the RSS for everyone and add tests (Fixes #529)