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
I made the cells not fill their full height. If they do, the error and git statuses for adjacent files don't look good. They bleed together, and the rounded corners look like little periodic indents. So, we need some vertical separation between the status components, and we want the status components to line up horizontally with the thing they're decorating ==> everything got one pixel shorter. Could experiment with 2px or more to see what it looks like -