message: Turn off the frame around all tab widgets in the SplitLayout
diff: @@ -283,6 +283,7 @@ export class SplitLayout {
  // Create a new TabWidget
  const newTabWidget = <TabWidget> document.createElement(TabWidget.TAG_NAME);
  + newTabWidget.setShowFrame(false);
  const newTabWidgetInfo: TabWidgetInfoNode = {
  type: "tabwidget",
  children: [],
  @@ -312,6 +313,7 @@ export class SplitLayout {
  if (splitterInfo.type === "splitter" && tabWidgetInfo.type === "tabwidget") {
  // Create a new TabWidget
  const newTabWidget = <TabWidget> document.createElement(TabWidget.TAG_NAME);
  + newTabWidget.setShowFrame(false);
  const newTabWidgetInfo: TabWidgetInfoNode = {
  type: "tabwidget",
  children: [],
  @@ -353,6 +355,7 @@ export class SplitLayout {
  // Create a new TabWidget
  const newTabWidget = <TabWidget> document.createElement(TabWidget.TAG_NAME);
  + newTabWidget.setShowFrame(false);
  const newTabWidgetInfo: TabWidgetInfoNode = {
  type: "tabwidget",
  children: tabWidgetInfo.children.slice(splitIndex),
  @@ -397,6 +400,7 @@ export class SplitLayout {
  // Create a new TabWidget
  const newTabWidget = <TabWidget> document.createElement(TabWidget.TAG_NAME);
  + newTabWidget.setShowFrame(false);
  const newTabWidgetInfo: TabWidgetInfoNode = {
  type: "tabwidget",
  children: tabWidgetInfo.children.slice(splitIndex),
  