[Doc] Fix unassociated doc strings

Before this commit, these doc strings were unassociated, which means
that the can appear at random places.  They are now associated with
their namespace an class.

src/Mod/Import/App/SketchExportHelper.h

@@ -20,7 +20,6 @@
  *                                                                         *
  ***************************************************************************/
 
-//! a class to assist with exporting sketches to dxf
 
 #include <Mod/Import/ImportGlobal.h>
 
@@ -35,6 +34,9 @@ class DocumentObject;
 namespace Import
 {
 
+/**
+ * A class to assist with exporting sketches to dxf.
+ */
 class ImportExport SketchExportHelper
 {
 public:

src/Mod/TechDraw/Gui/CommandHelpers.h

@@ -22,7 +22,6 @@
  *                                                                         *
  ***************************************************************************/
 
-//! CommandHelpers is a collection of methods for common actions in commands
 
 
 #ifndef COMMANDHELPERS_H
@@ -46,6 +45,9 @@ namespace TechDraw {
 class DrawView;
 class DrawViewPart;
 
+/**
+ * CommandHelpers is a collection of methods for common actions in commands.
+ */
 namespace CommandHelpers {
 TechDraw::DrawView* firstViewInSelection(Gui::Command* cmd);
 TechDraw::DrawView* firstNonSpreadsheetInSelection(Gui::Command* cmd);