added save functions to various classes

Each class is responsible for its own saving and loading from the XML data
in order to reduce the complexity of the save code.

app/common/rational.cpp

@@ -117,6 +117,11 @@ const intType &rational::denominator() const
   return denom;
 }
 
+QString rational::toString() const
+{
+  return QStringLiteral("%1/%2").arg(QString::number(numer), QString::number(denom));
+}
+
 //Assignment Operators
 
 const rational& rational::operator=(const rational &rhs)