documentation

Pull request #2748: ZBX-9370 Remember for 30 days option documented.

Merge in WEB/documentation from feature/ZBX-9370-7.0-D to release/7.0

* commit '1e36193c1c758db95ce97bd5beb7822f3e4e30ec':
  ZBX-9370 removed mentions of persistent cookie.
  ZBX-9370 Remember for 30 days option documented.