XD-2378 Add ability to logout using the Admin UI

* Add `/security/info` REST endpoint, providing security related meta information
* Add integration test for `/security/info` REST endpoint
* Add logout functionality to the Admin UI
  - Ensure the `/security/info` REST endpoint is executed before AngularJS boots
  - Make security meta information available to AngularJS
  - Provide UI components to log out
  - Show the currently logged in user (if logged in and authentication is enabled)
  - If not logged in, redirect to login page