Spreadsheet: support mapping protocol in PropertySheetPy

Read only mapping protocol support to retrieve a range of cell values.
Expects the key to be a string of either a single cell address or a
range.

src/Mod/Spreadsheet/App/PropertySheetPyImp.cpp

@@ -23,7 +23,7 @@
 
 #include "PreCompiled.h"
 
-#include "PropertySheet.h"
+#include "Mod/Spreadsheet/App/PropertySheet.h"
 
 // inclusion of the generated files (generated out of PropertySheetPy.xml)
 #include "PropertySheetPy.h"
@@ -31,6 +31,23 @@
 
 using namespace Spreadsheet;
 
+struct PropertySheetPyInit {
+
+    PyMappingMethods methods;
+
+    PropertySheetPyInit() {
+        methods.mp_length = 0;
+        methods.mp_ass_subscript = 0;
+        methods.mp_subscript = [](PyObject *o, PyObject *key) {
+            return static_cast<PropertySheetPy*>(o)->getPropertySheetPtr()->getPyValue(key);
+        };
+
+        PropertySheetPy::Type.tp_as_mapping = &methods;
+    }
+};
+
+static PropertySheetPyInit _PropertySheetPyInit;
+
 // returns a string which represents the object e.g. when printed in python
 std::string PropertySheetPy::representation(void) const
 {