feeling animated

Did some refactoring so that the CADisplayLink is created in the View Controller, calling to the GridView and SpriteGroup classes with the current frame update interval in an update method; and also added some animations for tiles and sprites.

The transforms are created in response to user interaction, but all the animation updates, movement updates and layer transformations are applied in the display link update method within a core animation transaction, so that everything is in sync and doesn’t flicker.