Update Aglio logo

Adds the new [Aglio logo](https://github.com/danielgtaylor/aglio/blob/master/images/aglio.png):

![screen shot 2014-12-13 at 7 27 12 pm](https://cloud.githubusercontent.com/assets/106826/5426378/56a6dcc4-8302-11e4-8715-03c40969ffbd.png)