Use layer_widget in Gerbview

Added sample gerber files for test (gerbview has problem with 2 files)

pcbnew/dialog_general_options.cpp

@@ -241,7 +241,7 @@ void WinEDA_PcbFrame::OnSelectOptionToolbar( wxCommandEvent& event )
         m_auimgr.Update();
         break;
 
-    case ID_TB_OPTIONS_SHOW_LAYERS_MANAGER_VERTICAL_TOOLBAR:
+    case ID_TB_OPTIONS_SHOW_MANAGE_LAYERS_VERTICAL_TOOLBAR:
         // show auxiliary Vertical layers and visibility manager toolbar
         m_show_layer_manager_tools = state;
         m_auimgr.GetPane( wxT( "m_LayersManagerToolBar" ) ).Show( m_show_layer_manager_tools );