Log out from PubSub Node

To logout from single node, user must send presence stanza with type unavailable:

<presence
    from='hag66@shakespeare.lit/pda'
    type='unavailable'
    to='pubsub.shakespeare.lit'>
  <pubsub xmlns='tigase:pubsub:1' node='princely_musings'/>
</presence>

Component will send events to all occupants as described:

<message from='pubsub.shakespeare.lit' to='francisco@denmark.lit' id='foo'>
  <event xmlns='http://jabber.org/protocol/pubsub#event'>
    <items node='princely_musings'>
      <item>
        <presence xmlns='tigase:pubsub:1' node='princely_musings' jid='hag66@shakespeare.lit/pda' type='unavailable'/>
      </item>
    </items>
  </event>
</message>

If component receives presence stanza with type unavailable without specified node, then component will log out user from all nodes he logged before and publish events.