Univention Corporate Server 4.0 erratum 236 (bugfix)

This update addresses the following issues:
  * The UCR variable mail/cyrus/auth/allowplaintext to (dis)allow plain
    text passwords over non-TLS connections has been added. The variable
    defaults to "no".
    Attention: This changes the previous default behaviour! Plain text
    authentication over unencrypted connections is now disabled by
    default. To revert to the old behaviour set
    mail/cyrus/auth/allowplaintext=yes resp.
    mail/dovecot/auth/allowplaintext=yes (Bug #38500).
  * Several changes related to dovecot integration (Bug #38479, #38707)
  * The UDM module policies/mailquota has been moved to the package
    univention-mail-cyrus. The UDM module will only be available if the
    UCS mail stack with cyrus is installed. No change in behaviour
    (Bug #38473).