424 hafas importer: extract KOORD parsing logic, unit tests and fix

Same as #423 (closed), extracted the parsing logic in a static function, wrote unit tests and then fixed 3 (!!) bugs. I have also put the ScopedCoordinatesSystemUser utility struct in a new header file in test/common as it was already duplicated in 2 files. I ended up not using it in my tests but kept the change anyway.