Sponsor refactor

part of PT story https://www.pivotaltracker.com/story/show/79559336
- replaced id with osra num on sponsor index page
- added osra_num and affiliate to sponsor show page

![screenshot from 2014-09-26 19 50 24](https://cloud.githubusercontent.com/assets/7509180/4425869/1b996610-45ae-11e4-83f8-3e4981c8d10d.png)
![screenshot from 2014-09-26 19 51 00](https://cloud.githubusercontent.com/assets/7509180/4425876/22cd2872-45ae-11e4-9d7e-d5e7653f7020.png)

Re: the word "affiliate" I think it's appropriate for this purpose. The other words I though of were "source" or "origin". I say let's keep it for now.