Changed mouseJoint example for touch based platforms

Changed the mouseJoint example to avoid using hoverEnabled: true, as it is not available on touch based platforms.
Now the mousejoint target position gets updated in the onPositionChanged handler.
I don't understand the need for these two variables. You're only using `rectanglesArray` to get at the rectangle at `rectangleIndex`, but then why would you have the array and the index at all? You could just have one `property Body pressedBody` and assign the `rectangleBody` to it directly where you are currently doing `rectangleIndex = index`.