improve IA of proofs#new and proofs#edit

This makes the pages for attaching a proof and editing a proof at least bearable to use. Code has been reviewed but looking for a second opinion.

Hi @j-schumacher, 

Would you be free to do a code review of this PR? I'm really looking to make sure my html tags are all closed and indented properly. A wrongly placed html tag could be a problem for javascript later. Let me know.

Best, 

;Akshat



**Attach a proof**
![screenshot 2014-04-09 15 11 49](https://cloud.githubusercontent.com/assets/331004/2660028/d56beac8-c01a-11e3-87fb-7439b3d22964.png)


**Update a proof**
![screenshot 2014-04-09 15 11 09](https://cloud.githubusercontent.com/assets/331004/2660019/b9bede98-c01a-11e3-8267-750921c61608.png)