OTR messages should be sent with no-copy, no-permanent-store, private #620

<message from='[email protected]/countesshousehold'
         to='[email protected]/veiled'>
  <body>?OTR?v23?...</body>
  <no-copy xmlns="urn:xmpp:hints"/>
  <no-permanent-store xmlns="urn:xmpp:hints"/>
  <private xmlns="urn:xmpp:carbons:2"/>
</message>