Added our copyright statement to xmlutils.cpp.
Added our copyright statement to xmlutils.cpp.

nickerso/libcellml,nickerso/libcellml,hsorby/libcellml,cellml/libcellml,hsorby/libcellml,cellml/libcellml,MichaelClerx/libcellml,hsorby/libcellml,MichaelClerx/libcellml,MichaelClerx/libcellml,nickerso/libcellml,cellml/libcellml,hsorby/libcellml,cellml/libcellml,nickerso/libcellml