Make new and edit file submit more uniform

DRY them up. UI changes:

- uppercased `Commit changes` to `Commit Changes` on both forms as per https://github.com/gitlabhq/gitlabhq/issues/7789
- change color from blue to green on the edit form (which differed from the new one: it shouldn't)

After:

![screenshot from 2014-10-03 00 12 33 commit changes new](https://cloud.githubusercontent.com/assets/1429315/4499383/b86fc894-4a81-11e4-8b4c-1cae8639e401.png)

Before:

![screenshot from 2014-10-02 23 54 19 commit changes before](https://cloud.githubusercontent.com/assets/1429315/4499384/c1c12690-4a81-11e4-8b34-2fcd28babb8e.png)