Add `meetingID` to `Hook` class

[lesha724]

It would be nice if property meetingID was added to the Hook class.

<response>
  <returncode>SUCCESS</returncode>
  <hooks>
    <hook>
      <hookID>12345678-1234-5678-1234-567812345678</hookID>
      <callbackURL><![CDATA[http://postcatcher.in/catchers/abcdefghijk]]></callbackURL>
      <meetingID><![CDATA[my-meeting</meetingID]]>> <!-- a hook created for this meeting only -->
      <permanentHook>false</permanentHook>
      <rawData>false</rawData>
    </hook>
    <hook>
      <hookID>01234567-89ab-cdef-0123-456789abcdef</hookID>
      <callbackURL><![CDATA[http://postcatcher.in/catchers/1234567890]]></callbackURL>
      <!-- no meetingID means this is a global hook -->
      <permanentHook>false</permanentHook>
      <rawData>false</rawData>
    </hook>
  </hooks>
</response>