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)
How are tasks embedded in the app resource? Don't they require `?embed=tasks` or something similar?