Path: added Path.fromShapes and Path.sortWires

* Path.fromShapes can now convert any number of shapes to Path with
optimzied travel distances. It internally uses Path.sortWires to
minimize travel distances, and also sort wires by its Z height in case
of sectioned wires.

* The above python function is impelmented in Path::Area class.

* Path::FeatureShape is rewrote to take advantage of these two
functions.

* Add Path::FeatureAreaView to partially display a Path::FeatureArea's
sections.

src/Mod/Path/App/FeatureAreaPyImp.cpp

@@ -46,7 +46,7 @@ PyObject* FeatureAreaPy::getArea(PyObject *args)
     if (!PyArg_ParseTuple(args, ""))
         return NULL;
 
-    return new AreaPy(new Area(getFeatureAreaPtr()->myArea));
+    return new AreaPy(new Area(getFeatureAreaPtr()->getArea()));
 }
 
 PyObject* FeatureAreaPy::setParams(PyObject *args, PyObject *keywds)