View files and directories

* Ability to look into files and folders for a certain commit
* Added button in commit menu
* File and folder views match the appearance of the diff page (fold/unfold as well)
* Binary files are downloaded instead of navigating to the view page
* User can navigate back to the diffs with the same button menu

Requirements git-server: https://github.com/devhub-tud/git-server/pull/25


![screen shot 2014-05-21 at 20 57 39](https://cloud.githubusercontent.com/assets/3469492/3045145/dd14b5b4-e119-11e3-90f4-e9c49468b7d1.png)
![screen shot 2014-05-21 at 20 57 57](https://cloud.githubusercontent.com/assets/3469492/3045146/dd270340-e119-11e3-9725-e0bed0c513b7.png)
![screen shot 2014-05-21 at 20 59 00](https://cloud.githubusercontent.com/assets/3469492/3045162/0209c1de-e11a-11e3-92d0-e21e60554b22.png)