#60 Image diff in staging

![screen shot 2013-10-29 at 23 24 56](https://f.cloud.github.com/assets/5281068/1434476/6824ab86-411b-11e3-8f61-ecff3c0683db.png)


Ungit now displays images in staging. Issue https://github.com/FredrikNoren/ungit/issues/60

Tested with JPG, GIF, PNG and BMP.

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* Image jumping was reduced, but it isn't completely eliminated.  I believe problem is that image stretches td when displayed and when "diffs" gets refreshed previous image is delete before new image is fully loaded.  Thus stretched td "jump" to small size and gets stretched back.  Not sure what is the best way to freeze the size of td once initial image is loaded in clean way.  I can quickly do some jquery hacks but that can't be a recommended approach.