FEM: Draft architecture of post data extraction with histogram example

src/Mod/Fem/App/FemPostObjectPy.xml

@@ -23,6 +23,13 @@ filename: str
     File extension is automatically detected from data type.</UserDocu>
             </Documentation>
         </Methode>
+        <Methode Name="getDataSet">
+            <Documentation>
+                <UserDocu>getDataset() -> vtkDataSet
+
+Returns the current output dataset. For normal filters this is equal to the objects Data property output. However, a pipelines Data property could store multiple frames, and hence Data can be of type vtkCompositeData, which is not a vtkDataset. To simplify implementations this function always returns a vtkDataSet, and for a pipeline it will be the dataset of the currently selected frame. Note that the returned value could be None, if no data is set at all.</UserDocu>
+            </Documentation>
+        </Methode>
 
     </PythonExport>
 </GenerateModel>