Ok I found out myself:
GateOne comes with a server where I can configure "50terminal.conf" file to execute every shell command or script. By telling him to execute consolecallback.py I can open the serial console of a kvm in browser. -> But I don't need this script after all - I can just use normal virsh -c qemu://host/system console vm-name as command in 50terminal.conf and don't need that script at all to get kvm-serial-console into the browser even more simple as by using the python programm...