Link to blob edit from tree view with row on hover visible links [Awaiting developper feedback]

So as to not clutter the UI, the link only appears when you hover the row for the given file:

![screenshot from 2014-11-17 17 19 25 row hover](https://cloud.githubusercontent.com/assets/1429315/5072916/5c6b7a9a-6e7e-11e4-8691-a187bf9b5fb9.png)

When you hover the edit icon, it becomes larger:

![screenshot from 2014-11-17 17 19 37 icon hover](https://cloud.githubusercontent.com/assets/1429315/5072920/652e03b4-6e7e-11e4-8eeb-d56bc8f5604a.png)

The links take up little space, and disappear completely on `xs` screens.

The only part missing is to determine if the blob is text or not, this should be done on the same AJAX request that gets the commit data so as to not halt page loading.