+ support of Python feature classes without an execute() method

+ if execute() method of Python feature is missing or if it returns false call the execute() method of the C++ feature
+ fix SketchObjectPython

src/Mod/Sketcher/App/SketchObject.cpp

@@ -49,6 +49,7 @@
 #include <boost/bind.hpp>
 
 #include <App/Document.h>
+#include <App/FeaturePythonPyImp.h>
 #include <Base/Writer.h>
 #include <Base/Reader.h>
 #include <Base/Tools.h>
@@ -4016,6 +4017,13 @@ PROPERTY_SOURCE_TEMPLATE(Sketcher::SketchObjectPython, Sketcher::SketchObject)
 template<> const char* Sketcher::SketchObjectPython::getViewProviderName(void) const {
     return "SketcherGui::ViewProviderPython";
 }
+template<> PyObject* Sketcher::SketchObjectPython::getPyObject(void) {
+    if (PythonObject.is(Py::_None())) {
+        // ref counter is set to 1
+        PythonObject = Py::Object(new FeaturePythonPyT<SketchObjectPy>(this),true);
+    }
+    return Py::new_reference_to(PythonObject);
+}
 /// @endcond
 
 // explicit template instantiation