Use css persona buttons on login
Change badge accept button to CSS as well
Merge pull request #756 from stenington/649-button-css

CSS persona sign-in buttons

closes #649
Closes #666: Redirecting from /backpack/login when logged in
Return on redirect from login, and update backpack controller to call redirect(status, location) throughout
Merge pull request #754 from stenington/666-issue-of-the-beast

Redirecting from /backpack/login when logged in

closes #666
Discover persona audience from request.

* We are going to be serving the backpack from two locations for a
  little while: beta.openbadges.org, and backpack.openbadges.org. This
  means that the audience needs to be derived from the request rather
  than from the server configuration, so that's what this commit does.

* Also, I've done a lot of refactoring to make things generally better,
  hopefully.
Fix some argument orders.