Navigator should use a different icon while panning

The Navigator uses the same hand icon regardless whether panning
the red square or not, this branch tries to fix that, #4738
Includes a cleanup of icon names, i.e. the crosshair should not be
called the hand.

rtgui/curveeditor.cc

@@ -443,5 +443,5 @@ CursorShape CurveEditor::getCursor(const int objectID)
         return CSResizeHeight;
     }
 
-    return CSOpenHand;
+    return CSHandOpen;
 }