Fix Barcode encoding

This fixes a parameter order bug in the barcode encoding that lead to invalid barcodes. It also moves the responsibility of assigning the barcode particle away from the EventGenerator into the dedicated process generators. The EventGenerator now only merges the output from multiple process generators and fixes the vertex index but leaves everything else untouched. Previously, the responsibility was under-defined.

I still do not understand the meaning of some of the barcode components; but this has to be fixed in a another MR.