Added freeware icon for platypus .app


![xnomad icns](https://f.cloud.github.com/assets/4357009/656339/3be65e9c-d529-11e2-978d-8f5d2f19955e.png)
I added a freeware icon so that the platypus compile looks halfway decent while it sits in the applications folder and dock (assuming you're using my "don't run in the background commit). The compile gives a warning saying that the icns file "isn't identified as apple", and so I'll fix that as soon as I figure out what that means(!).