* Add a way for users to temporarily deactivate their accounts, in a
recoverable way should they decide to return later.
* A deactivated account may log in but have limited options: to
reactivate their account, permanently delete it, or log out.
* Fix several bugs around the display of comments, messages and
forum threads for disabled, banned, or blocked users:
* Messages (inbox and sentbox) will be hidden and the unread indicator
will not count unread messages the user can't access.
* Comments on photos and forum posts are hidden, and top-level threads
on the "Newest" tab will show "[unavailable]" for their text and
username.
* Your historical notifications will hide users who are blocked, banned
or disabled.
* Add a "Friends" tab to user profile pages, to see other users' friends.
* The page is Certification Required so non-cert users can't easily
discover any members on the site.
Implement block lists. They work like friend lists but are unidirectional,
but take effect in both directions (blocker and blockee can not see one
another on the site -- except admin users can always see all users).
* Profile page says 404
* User gallery says 404
* User search page filters out blocked users
* Compose endpoint blocks sending messages to blocked users (except admin)
* Site Gallery filters photos by blocked (and uncertified) users
* Inbox page hides chat list for blocked users (can still read the chat
history if you have a link to the old thread)
