When an anonymous users tries to go to the new upload page, direct them
to the login page instead of showing them an "Access Denied" error.
Fixes complaints from SEO tools about linking to pages that return a 403
error.
* 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.
