Changes:
* Make it so you can click or hover over a post's favorite count to see
the list of public favorites.
* Remove the "Show »" button next to the favorite count.
* Make the favorites list visible to all users. Before favorites were
only visible to Gold users.
* Make the /favorites page show the list of all public favorites,
instead of redirecting to the current user's favorites.
* Add /posts/:id/favorites endpoint.
* Add /users/:id/favorites endpoint.
This is for several reasons:
* To make viewing favorites work the same way as viewing upvotes.
* To make posts load faster for Gold users. Before, we loaded all the
favorites when viewing a post, even when the user didn't look at them.
This made pageloads slower for posts that had hundreds or thousands of
favorites. Now we only load the favlist if the user hovers over the favcount.
* To make the favorite list visible to all users. Before, it wasn't
visible to non-Gold users, because of the performance issue listed above.
* To make it more obvious that favorites are public by default. Before,
since regular users could only see the favcount, they may have
mistakenly believed other users couldn't see their favorites.
* Allow Member-level users to vote.
* Don't allow Banned or Restricted users to create favorites any more.
Banned and Restricted users aren't allowed to upvote or favorite any
more to prevent sockpuppet accounts from upvoting even after they're
banned.
Stop updating the fav_string attribute on posts. The column still exists
on the table, but is no longer used or updated.
Like the pool_string in 7d503f08, the fav_string was used in the past to
facilitate `fav:X` searches. Posts had a hidden fav_string column that
contained a list of every user who favorited the post. These were
treated like fake hidden tags on the post so that a search for `fav:X`
was treated like a tag search.
The fav_string attribute has been unused for search purposes for a while
now. It was only kept because of technicalities that required
departitioning the favorites table first (340e1008e) before it could be
removed. Basically, removing favorites with `@favorite.destroy` was
slow because Rails always deletes object by ID, but we didn't have an
index on favorites.id, and we couldn't easily add one until the
favorites table was departitioned.
Fixes#4652. See https://github.com/danbooru/danbooru/issues/4652#issuecomment-754993802
for more discussion of issues caused by the fav_string (in short: write
amplification, post table bloat, and favorite inconsistency problems).
Add a Restricted user level. Restricted users are level 10, below
Members. New users start out as Restricted if they sign up from a proxy
or an IP recently used by another user.
Restricted users can't update or edit any public content on the site
until they verify their email address, at which point they're promoted
to Member. Restricted users are only allowed to do personal actions
like keep favorites, keep favgroups and saved searches, mark dmails as
read or deleted, or mark forum posts as read.
The restricted state already existed before, the only change here is
that now it's an actual user level instead of a hidden state. Before it
was based on two hidden flags on the user, the `requires_verification`
flag (set when a user signs up from a proxy, etc), and the `is_verified`
flag (set after the user verifies their email). Making it a user level
means that now the Restricted status will be shown publicly.
Introducing a new level below Member means that we have to change every
`is_member?` check to `!is_anonymous` for every place where we used
`is_member?` to check that the current user is logged in.
