MODE-2340: Can not log out from Repository Explorer application

This PR implements logout procedure:
- remove credentials; 
- resets view to the entry page with repositories;
- invalidates existing HTTP session
There is one thing that bothers me. We suppose that user can be authenticated over HTTP and thus we need to invalidate the HTTP session always. But from other hand HTTP sessions is used by explorer to keep parameters and a reference to the current path in particular. To be able to stay on the same page I guess we need to perfom test for anonymous access during the logout procedure (before session invalidation) and return true or false as a flag for final action (stay on page or show repositories) raither then trying to point browser and catch exception.