Improve UI for list of changed files

* fix paddings
* re-use system colors

## Before

![Screenshot_2015-10-01_12.46.24](https://gitlab.com/gitlab-org/gitlab-ce/uploads/3a02fe2beb47637c664eb914dbec352c/Screenshot_2015-10-01_12.46.24.png)


## After

![Screenshot_2015-10-01_12.54.39](https://gitlab.com/gitlab-org/gitlab-ce/uploads/39b1bf78983b862b559fcc89c52d5690/Screenshot_2015-10-01_12.54.39.png)


cc @skyruler 
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !1484