* Users with private profiles or no public photo at all are considered
to be Shy Accounts and are isolated from the non-shy profiles.
* Restrictions include:
* Site Gallery shows only them + their friends' photos.
* User Galleries: must be a friend or had private photos granted to
see a user's gallery page.
* DMs: can not initiate a DM to a non-shy member (other shy members
OK).
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)
