Document risk of exposing data to anonymous users via profiles

See https://issues.civicrm.org/jira/browse/CRM-18122

It is much too easy to grant permissions that inadvertently expose data.

Barring improvements to profiles and/or permissions (and even if they were improved) we should have clear documentation on the risk of doing so, and steps you can take to avoid it.

I should be discussed and/or cross referenced in

• http://docs.civicrm.org/user/en/stable/initial-set-up/permissions-and-access-control/ and
• http://docs.civicrm.org/user/en/stable/initial-set-up/security/
• http://docs.civicrm.org/user/en/stable/organising-your-data/profiles/

When working on this, it might be a good time to merge information from the following wiki pages into the book and delete the wiki page:

• https://wiki.civicrm.org/confluence/display/CRMDOC/Default+Permissions+and+Roles
• https://wiki.civicrm.org/confluence/display/CRMDOC/Access+Control+Context+and+Overview

Once complete, it probably makes sense to update UI references to the documentation in appropriate pages like the profiles config pages.