* Rename 'privacy mode' to 'private favorites'.
* Make the private favorites setting only hide favorites, not favgroups
and not the user's uploads on their profile page.
* Make the favgroup is_public flag default to true instead of false and
fix existing favgroups to be public if the user didn't have privacy mode
enabled before.
* List _all_ public favgroups on the /favorite_groups index, not just
favgroups belonging to the current user.
* Add a /users/<id>/favorite_groups endpoint.
* Open recommendations to all users (not just gold).
* Show recommendations on all posts (not just posts after 2017).
* Allow users to browse recommendations for other users.
* Increase number of recommended posts returned.
* Change endpoints to /recommended_posts?user_id=1234 and
/recommended_posts?post_id=1234 and add json/xml support.
* Fix inconsistencies in how wiki pages were linked.
* Link directly to the wiki instead of to a title search that is expected
to redirect to the wiki.
* Always display 'Saved searches' link in subnav bar, even if the user
hasn't created any saved searches yet.
* Eliminate use of `has_saved_searches` bitpref on users.
Make /favorites redirect to a ordfav:<user> search instead of having a
separate view just for favorites. This duplicated a lot of code for no
good reason.
