Sketcher: implement command to decrease degree of a B-spline

src/Mod/Sketcher/App/SketchObjectPyImp.cpp

@@ -1396,6 +1396,24 @@ PyObject* SketchObjectPy::increaseBSplineDegree(PyObject *args)
     Py_Return;
 }
 
+PyObject* SketchObjectPy::decreaseBSplineDegree(PyObject *args)
+{
+    int GeoId;
+    int incr = 1;
+
+    if (!PyArg_ParseTuple(args, "i|i", &GeoId, &incr))
+        return 0;
+
+    if (this->getSketchObjectPtr()->decreaseBSplineDegree(GeoId, incr)==false) {
+        std::stringstream str;
+        str << "Degree decrease failed for: " << GeoId;
+        PyErr_SetString(PyExc_ValueError, str.str().c_str());
+        return 0;
+    }
+
+    Py_Return;
+}
+
 PyObject* SketchObjectPy::modifyBSplineKnotMultiplicity(PyObject *args)
 {
     int GeoId;