DESCRIPTION:

Eccet can be fed with camera position (see bus) data by
udp connections. As multiple instances of Eccet are allowed
to be run at the same time, the ports cannot be static, but
are assigned in a "first free port in a range" manner.
Thus if you want to connect to a specific voxren instance,
you have to query this value.
- listenport (int) the port on which the position bus listens.