Part: changes to Part Module

* Added Part::Feature::getTopoShape/getShape() function that can obtain
  shape from any object with proper implementation of getSubObject(). It
  can even construct compound from group object with proper implementation
  of getSubObjects().

* Modified ViewProviderExt to work on any object, because it now obtain
  the shape using Part::Feature::getShape()

* Modified various Part features to obtain base/tool shapes using
  Part::getShape(), which allows them to be any type of object,
  including Link and groups.

* Modified various Part command to relax type requirement on selected
  objects.

* Add support of link and group to dimension, and add dimension refresh
  command

* Support link and group in simple command command, and add a few more
  copy command variations.

* Add special handling of 'Shape' attribute in PropertyContainerPy and
  use Part::Feature::getShape() to return shape for any object without
  Shape property. This allows many python feature work with any object
  without modification.

* GeometrySurface/CurvePy, add convenience attribute 'Rotation'

* TopoShapePy:

    * Extended support of sub shape attribute, e.g. Compound1, Solid2,
      SubShape3 ('SubShape' is used to access child shape of a compound)

    * makeWires(), new API to sort and return wires given a list of edges.

    * transformed/translated/rotated/scaled(), return a new shape with
      some transformation.

    * findPlane(), find the plane of a planar shape

    * isCoplanar(), check if two shape are coplanar

src/Mod/Part/App/FeatureOffset.cpp

@@ -77,7 +77,7 @@ short Offset::mustExecute() const
 App::DocumentObjectExecReturn *Offset::execute(void)
 {
     App::DocumentObject* source = Source.getValue();
-    if (!(source && source->getTypeId().isDerivedFrom(Part::Feature::getClassTypeId())))
+    if (!source)
         return new App::DocumentObjectExecReturn("No source shape linked.");
     double offset = Value.getValue();
     double tol = Precision::Confusion();
@@ -86,7 +86,7 @@ App::DocumentObjectExecReturn *Offset::execute(void)
     short mode = (short)Mode.getValue();
     short join = (short)Join.getValue();
     bool fill = Fill.getValue();
-    const TopoShape& shape = static_cast<Part::Feature*>(source)->Shape.getShape();
+    const TopoShape& shape = Feature::getShape(source);
     if (fabs(offset) > 2*tol)
         this->Shape.setValue(shape.makeOffsetShape(offset, tol, inter, self, mode, join, fill));
     else