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.
* 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).
Fix discrepancy between index action and show action. The index
action allowed members to see name changes for undeleted users, but the
show action didn't.
