Detector2D now parameterized through width and center in phi,alpha (#854)

Some code duplication in the GUI (Axis -> Span property and form), to be revised later.

Resolves #854 (closed).

GUI/Model/Descriptor/SpanProperty.cpp

@@ -22,7 +22,9 @@ namespace Tag {
 const QString Nbins("Nbins");
 const QString Width("Width");
 const QString Center("Center");
-const QString ExpandGroupbox("ExpandGroupbox"); // obsolete since v22.0
+const QString Min("Min"); // from AxisProperty pre v22
+const QString Max("Max"); // from AxisProperty pre v22
+const QString ExpandGroupbox("ExpandGroupbox"); // from AxisProperty pre v22
 
 } // namespace Tag
 } // namespace
@@ -48,7 +50,7 @@ Scale SpanProperty::createAxis(const std::string& name) const
 
 void SpanProperty::writeTo(QXmlStreamWriter* w) const
 {
-    XML::writeAttribute(w, XML::Attrib::version, uint(2));
+    XML::writeAttribute(w, XML::Attrib::version, uint(3)); // forked from AxesProperty v3
 
     // nbins
     w->writeStartElement(Tag::Nbins);