Adds Animation to the MapCube object.

This has overlap with PR #384.

This can be run using the following code

```python
cube = MapCube(*maps)
ani, [start, stop] = cube.plot()

stop.on_clicked(ani._stop)
start.on_clicked(ani._start)

plt.show()
```

Note: For some reason I can not determine, if you connect the buttons to the animation methods inside MapCube.plot() they don't work! Suggestions please!

Also I added the colorbar option to plot() in MapCube because if you use the buttons it will not position the colorbar correctly.

![animation_result](https://f.cloud.github.com/assets/1391051/64373/f09a034c-5e42-11e2-865f-e9570ad671e3.png)