Make blob new and edit file editors more uniform

DRY them up. The UI changes is:

- remove cancel button from file edit header: there is already a Cancel button the bottom of the page, which is the standard place for cancel buttons

- add branch to new file edit. Already present on the edit, so let's make it uniform.

After edit: no cancel:

![screenshot from 2014-10-03 14 17 30 factor editor after](https://cloud.githubusercontent.com/assets/1429315/4505639/716470e0-4af8-11e4-81ce-91f9512edc64.png)

Before edit:

![screenshot from 2014-10-03 14 25 18 blob edit before](https://cloud.githubusercontent.com/assets/1429315/4505642/782e0e68-4af8-11e4-8fda-b7a2ba55f445.png)

After new (has branch on header):

![screenshot from 2014-10-03 14 24 44 blob new after](https://cloud.githubusercontent.com/assets/1429315/4505647/7f92d10c-4af8-11e4-921a-ffc6854e13d9.png)

Before new:

![screenshot from 2014-10-03 14 25 29 blob new before](https://cloud.githubusercontent.com/assets/1429315/4505653/8663c40a-4af8-11e4-89f5-d8b730720683.png)