* Let moderators see name changes for deleted users on the user name
change requests index and show pages. Before they could see name changes
for deleted users on user profiles, but not on the user name changes index.
* Let members see previous names on profile pages. Before they could see
previous names on the user name changes index, but not on profile pages
(ref: #4382).
Refactor how model visibility works in index actions:
* Call `visible` in the controller instead of in model `search`
methods. This decouples model visibility from model searching.
* Explicitly pass CurrentUser when calling `visible`. This reduces
hidden dependencies on the current user inside models.
* Standardize on calling the method `visible`. In some places it was
called `permitted` instead.
* Add a `visible` base method to ApplicationModel.
* 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.
If Post.fast_count returns nil, then the link_to call becomes
link_to(nil, <posts_path>) so the link text becomes the url itself,
which isn't what we want.
Instead the count is displayed as a '?' mark to indicate that we don't
know the true count.
* Allow mousing over the upload limit on profile pages to show the full
formula for the upload limit calculation. In particular, show how the
upload limit multiplier is derived from the deletion confidence.
* Refactor to avoid duplicating upload limit calculations in the
presenter, as much as possible.
