#60 Image files in staging

![screen shot 2013-10-21 at 22 33 31](https://f.cloud.github.com/assets/5281068/1405443/94f57f08-3d2b-11e3-9180-458f9590c10c.png)

Ungit now displays images in staging. Issue https://github.com/FredrikNoren/ungit/issues/60

Tested with JPG, GIF, PNG and BMP.