Add option to force port

[ChillerDragon]

Either as normal tem setting or even as start script argument. Add config to force the port which then gets passed to the teeworlds server as econ port. Also allow the value random.

The use case for this is security through non default/changing ports. And no port jamming during fast restarts (saves nerves and time during development).

sh_force_port=8303
sh_force_port=random