Fix status bar overlap on iOS 7

This uses an adapted version of [this code found on SO][1]. It has been modified so that the existing code (which performs a similar status bar fix for iOS 6) continues to operate for those using an older version of iOS.

I originally attempted to fix this in the javascript, but the way junior.css uses position: fixed to layout the page seemed to resist my attempts to change it.

Closes #2 

@struan Does this look like a reasonable solution to this issue? Or would it be better for me to figure out how to do this in js/css with junior?

### iOS 6

![screen shot 2013-11-06 at 17 46 34](https://f.cloud.github.com/assets/22996/1484844/8d3c972a-470c-11e3-9237-354bdbd8868b.png)

### iOS7

![screen shot 2013-11-06 at 17 46 48](https://f.cloud.github.com/assets/22996/1484847/92165d1c-470c-11e3-91b9-9780750e7bb8.png)


[1]: http://stackoverflow.com/a/19249775/372120