Fix writeXMLHeader hiding overloaded virtual function in base class

According to signature at base class the first argument to function is
passed not as a value, but as a reference. Change it accordingly to
match the signature in base class.

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
Fix ChamberLocationSpec re-deleclaratin as class

According to the header, ChamberLocationSpec is not a class, but a
struct. Change forward declarations accordingly.

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>