correct PixelGeoModelXml methods so that they correctly override versions called in GeoModelXml
As in the title; some important methods which should override base class implementations in GeoModelXml so that the appropriate version will get called, were not doing so because they were given different names. This corrects the names so that when running a Pixel geometry based on GeoModelXml, sensitive detectors can successfully be added.
At the same type, the necessary name for SensorClass which should be used in the geometry Xml when defining sensitive volumes is set to "PixelModule_Sensitive" instead of "PixelModule" since the latter is already used elsewhere in the Xml definitions. See here for an example.