Implementation of the following issues:

1) 0022385: [CEA 975] The icon "Clipping" is missing in OCC view
2) 0021793: [CEA 625] Clipping : from coordinates or from bounding box
3) 0021792: [CEA 624] Keep the clipping

src/GEOMBase/GEOMBase_Helper.cxx

@@ -341,6 +341,9 @@ void GEOMBase_Helper::displayPreview( GEOM::GEOM_Object_ptr object,
   SALOME_Prs* aPrs = getDisplayer()->BuildPrs( object );
   if ( aPrs == 0 || aPrs->IsNull() )
     return;
+    
+  // Make preview not clippable
+  aPrs->SetClippable (false);
 
   // Display prs
   displayPreview( aPrs, append, update );