Move new blob commit message textarea below editor

- match edit blob view
- you enter the commit message *after* you make the modifications

After:

![screenshot from 2014-10-03 00 28 09 new blob commit below after](https://cloud.githubusercontent.com/assets/1429315/4499501/91e9d79e-4a83-11e4-9730-ecfbad5599ac.png)

Before:

![screenshot from 2014-10-03 00 27 49 new blob commit below before](https://cloud.githubusercontent.com/assets/1429315/4499503/995ec52a-4a83-11e4-8d46-a83a0eb60981.png)