Initialize padding while creating a toolbar.

If padding value (stored in m_toolPacking) has been assigned prior to creating the toolbar (with SetToolPacking) then apply this padding to just created toolbar.
Otherwise initialize this variable with current padding retrieved from the toolbar to let GetToolPacking return proper padding value.
Implemented new method MSWSetPadding() to set padding for native toolbar.

include/wx/msw/toolbar.h

@@ -136,6 +136,8 @@ protected:
     // get the Windows toolbar style of this control
     long GetMSWToolbarStyle() const;
 
+    // set native toolbar padding
+    void MSWSetPadding(WXWORD padding);
 
     // the big bitmap containing all bitmaps of the toolbar buttons
     WXHBITMAP m_hBitmap;