[#78845544] sort users based on relationship to paper

#### admin:

![oct 28 2014 15 43](https://cloud.githubusercontent.com/assets/1903518/4815887/c50568bc-5eda-11e4-95a0-cd8de7033222.gif)

#### non-admin:

![oct 28 2014 15 43-non-admin](https://cloud.githubusercontent.com/assets/1903518/4815898/ccd971b4-5eda-11e4-90ed-600ab6e76fa3.gif)

The goal is to prevent leaking to a non-admin user who might be a reviewer on a paper (for example).

This means:

- when a user without the admin bit set views the drop down, they should only see collaborators, but not reviewers, admins, or editors
- when a user with the admin bit set views the drop down, they can see all users with a role to the paper

By my reading of the code, if a user is not a site admin, they will only see users with roles to this paper (which includes editors, reviewers, and so on).

Two changes are required:
- if a user is not an admin, they cannot see reviewers and editors (any role, except collaborator), plus they can see everyone else in the system
- `current_user.site_admin?` is insufficient here, what we want to know is whether the current user has admin rights for this journal

Something like this will benefit greatly from a spec demonstrating the intent.

Let me know if you'd like to jump on a Hangout to discuss this.