Process messages from the event stream.

def process_msg(self, msg):
        """Process messages from the event stream."""
        jmsg = json.loads(msg)
        msgtype = jmsg['MessageType']
        msgdata = jmsg['Data']

        _LOGGER.debug('New websocket message recieved of type: %s', msgtype)
        if msgtype == 'Sessions':
            self._sessions = msgdata
            # Check for new devices and update as needed.
            self.update_device_list(self._sessions)
        """
        May process other message types in the future.
        Other known types are:
        - PlaybackStarted
        - PlaybackStopped
        - SessionEnded
        """