Set Stage always on top

A test can fail if a mouse interaction is involved and the stage is not in front.

Author: Jugen

richtextfx/src/integrationTest/java/org/fxmisc/richtext/InlineCssTextAreaAppTest.java

@@ -23,6 +23,7 @@ public void start(Stage stage) throws Exception {
         scene = new Scene(area);
         this.stage = stage;
 
+        stage.setAlwaysOnTop(true);
         stage.setScene(scene);
         stage.setWidth(400);
         stage.setHeight(400);