[TD]reduce number of tiles for svg hatching

- reduce the size of the overlay area from 200% to an
  adjustable size with a default of 125%.

src/Mod/TechDraw/App/Preferences.h

@@ -102,6 +102,8 @@ public:
 
     static bool autoCorrectDimRefs();
     static int scrubCount();
+
+    static double svgHatchFactor();
 };
 
 }//end namespace TechDraw