fix: set default splitter position to 50

Close #75

Author: Felipe Lang

src/main/java/com/flowingcode/vaadin/addons/demo/TabbedDemo.java

@@ -312,6 +312,7 @@ public void setOrientation(Orientation orientation) {
     splitOrientation = orientation;
     if (currentLayout != null) {
       currentLayout.setOrientation(orientation);
+      currentLayout.setSplitterPosition(50);
     }
     orientationCB.setValue(Orientation.HORIZONTAL.equals(orientation));
   }