Start to take better control over the authentication and authorization
systems of the front end.

- Remove dependency on Annotator Auth plugin. With this change,
  Annotator is completely gone from the Angular application.

- Use angular-jwt and its http interceptor to ensure that auth tokens
  are up-to-date and auth token requests block store requests.

- With the interceptor in place, it's no longer necessary to resolve
  auth before the ng-view controllers.

- Use the session directly for getting the current user. This is in
  line with what is likely to happen for groups, too, soon.