Paginate sync sessions.

This will help debug @mikewray 's syncing issues; currently we can't see the necessary data in the `device_management` view because there is no pagination of sync sessions.

Now, default is 10 sync sessions per page, and we get pagination.

@aronasorman This is a straightforward feature request, and an answer for @mikewray depends on this, so I'd like to push this through today if possible.

![image](https://cloud.githubusercontent.com/assets/4072455/2830313/983beff2-cfad-11e3-8006-bcaa3cff432c.png)