Part/Sketcher: Refactor Geometry Extensions copy/save/restore AND attachment notification

=========================================================================================

- Long overdue refactor to avoid repetition during save/restore and copy.
- New interface to notify an extension when it is attached. It also enables the extension to gain
a pointer to the geometry container. This is intended to extend the functionality already existing
in Part::Geometry.

src/Mod/Part/App/GeometryExtension.cpp

@@ -45,12 +45,39 @@ PyObject* GeometryExtension::copyPyObject() const
     return static_cast<GeometryExtensionPy *>(obj.ptr())->copy(tuple.ptr());
 }
 
+void GeometryExtension::copyAttributes(Part::GeometryExtension * cpy) const
+{
+    cpy->setName(this->getName()); // Base Class
+}
+
 TYPESYSTEM_SOURCE_ABSTRACT(Part::GeometryPersistenceExtension,Part::GeometryExtension)
 
-void GeometryPersistenceExtension::restoreNameAttribute(Base::XMLReader &reader)
+void GeometryPersistenceExtension::restoreAttributes(Base::XMLReader &reader)
 {
     if(reader.hasAttribute("name")) {
         std::string name = reader.getAttribute("name");
         setName(name);
     }
 }
+void GeometryPersistenceExtension::saveAttributes(Base::Writer &writer) const
+{
+    const std::string name = getName();
+
+    if(name.size() > 0)
+        writer.Stream() << "\" name=\"" << name;
+
+}
+
+void GeometryPersistenceExtension::Save(Base::Writer &writer) const
+{
+    writer.Stream() << writer.ind() << "<GeoExtension type=\"" << this->getTypeId().getName();
+
+    saveAttributes(writer);
+
+    writer.Stream() << "\"/>" << std::endl;
+}
+
+void GeometryPersistenceExtension::Restore(Base::XMLReader &reader)
+{
+    restoreAttributes(reader);
+}