files view UX changes as per the mock

Re-work the UI for the files view to match the mock. This:

- changes the error and git decorations to be full height and 8px wide
- docks them on the sides (git status on the right, errors on the left). The mock only had space for errors (on the right)
- make the selection inset on the left and right, and have 2px rounded corners

I had to move the files status div up the component hierarchy a bit so that it could be docked on the left (instead of being docked on the left of the file name component). Also tweaked spacings a bit to line things up visually.

![screen shot 2014-06-14 at 3 12 58 pm](https://cloud.githubusercontent.com/assets/1269969/3279824/93ceae42-f41e-11e3-9c31-6cce4a98588f.png)

![screen shot 2014-06-14 at 3 13 08 pm](https://cloud.githubusercontent.com/assets/1269969/3279826/93cf7552-f41e-11e3-9204-ffbc99ceef81.png)

![screen shot 2014-06-14 at 3 13 38 pm](https://cloud.githubusercontent.com/assets/1269969/3279825/93cefcbc-f41e-11e3-89e5-09293d3d68b1.png)

@dinhviethoa
Use `margin: 0 16px;` (probably less clear but that's Chrome standard).