Enhancement : Layers merge

Added drawing test + fixed drawing test runner on Mac OS X

src/js/devtools/DrawingTestPlayer.js

@@ -101,6 +101,10 @@
     var screenCoordinates = pskl.app.drawingController.getScreenCoordinates(recordEvent.coords.x, recordEvent.coords.y);
     event.clientX = screenCoordinates.x;
     event.clientY = screenCoordinates.y;
+    if (pskl.utils.UserAgent.isMac && event.ctrlKey) {
+       event.metaKey = true;
+    }
+
     if (event.type == 'mousedown') {
       pskl.app.drawingController.onMousedown_(event);
     } else if (event.type == 'mouseup') {

test/drawing/DrawingTests.browser.js

@@ -4,6 +4,7 @@
   "color.picker.json",
   "frames.fun.json",
   "layers.fun.json",
+  "layers.merge.json",
   "lighten.darken.json",
   "move.json",
   "pen.secondary.color.json",

test/drawing/DrawingTests.casper.js

@@ -3,6 +3,7 @@
   "color.picker.json",
   "frames.fun.json",
   "layers.fun.json",
+  "layers.merge.json",
   "move.json",
   "pen.secondary.color.json",
   "squares.circles.json",