PartDesign: New features AdditiveHelix and SubtractiveHelix

These features, based on the code for the Pipe class, allow the user
to simply create a helical sweep within PartDesign workbench.

Sample application is threads, springs, coils, augers, etc.

Also, remove needless requirement for positive cone angle on helixes.

Thanks to @bitacovir for helping with the icons
Thanks to @chennes for review
Thanks to @vosk for review
Thanks to @wwmayer for review

Enforce that links stay within scope for ProfileBased features
This also ensures that the Body itself is not used for creating features within
the body, causing a "Graph not a DAG" error.

src/Mod/PartDesign/App/AppPartDesign.cpp

@@ -59,6 +59,7 @@
 #include "FeatureLoft.h"
 #include "ShapeBinder.h"
 #include "FeatureBase.h"
+#include "FeatureHelix.h"
 
 namespace PartDesign {
 extern PyObject* initModule();
@@ -116,6 +117,9 @@ PyMOD_INIT_FUNC(_PartDesign)
     PartDesign::Loft                        ::init();
     PartDesign::AdditiveLoft                ::init();
     PartDesign::SubtractiveLoft             ::init();
+    PartDesign::Helix                       ::init();
+    PartDesign::AdditiveHelix               ::init();
+    PartDesign::SubtractiveHelix            ::init();
     PartDesign::ShapeBinder                 ::init();
     PartDesign::SubShapeBinder              ::init();
     PartDesign::Plane                       ::init();