Bug fix/update app bg

Fixing bug, where Marathon would not update running tasks in app list in background when changing number of instances in app modal:

[![Marathon showing more running tasks than actually running](http://cl.ly/image/1x1D0h0x180s/Image%202014-08-25%20at%2014.03.19.png)](http://cl.ly/image/1x1D0h0x180s/Image%202014-08-25%20at%2014.03.19.png)
Does this need to be handled as a callback? If `setState` is called and then `onShowTaskDetails` is called, they will likely happen fast enough that the rendering is batched.