Add an animation example

This PR show how to use `ngAnimate` to animate the resizing of a map. The main problem is to avoid distorting the map during the animation. In this example a `requestAnimationLoop` calling `map.udpateSize` is used to address that problem.

Ultimately it would be good to have something in `ngeo` for that, but I don't know what that could be at this point.

Please review.