Add gems devise_openid_authenticatable and rack-openid to project, ref #9
Change devise user model and login, ref #9

  * add string identity_url to model
  * remove undesired devise options (like registration)
  * change sing_in view to openid only
Add logout button to navigation bar if logged in, ref #9
Restrict view access to signed in users only, ref #9

  * redirects to sign_in page if not logged in
Redirect user to their previous called page after login, ref #9
Restrict OpenID provider to HPI, ref #9
Add a sign-in-call to all controller tests, to fix all crashes, ref #9
add RSpec gem and helpers
add RSpec test for tasks to test authentication
Merge remote-tracking branch 'biber-fork/dev' into Biber/feature/authentication, ref #9
Merge branch 'Biber/feature/authentication' into dev, ref #9