Implement sponsor feature and add adiitonal scenarios for earlier features

Part of PT story https://www.pivotaltracker.com/story/show/76232594

- add more tests to admin users feature
- add additional scenario to partner featue
- added sponsor feature 
- fix delete links being show for sponsors by active admin
- added linked name to sponsor index view
- refactored authenticated user step into background
Like in the `partner.feature`, I would like some more detailed tests for the index and show pages.