further develop support for getting station names

* if we got no data from the server in the haltestelle.processabfahrten() method, we call haltestelle.getHaltestellen() method
* when we got data from the server in the haltestelle.getHaltestellen() method, we call the haltestelle.processHaltestellen() method
* in the haltestelle.processHaltestellen() method we process the gotten data and print it into the output area of the html file