Finished integration with Google Cloud Services. Users are now saved as a file on GCS.

Implemented the Vaadin Navigator instead of my custom navigator.
Merge branch 'master' of https://github.com/janmilinds/VaadinExcercise into ErnoBranch
Centered the login components; looks prettier. The session also remembers which user is logged on by a static field in User. Every time the Login screen is entered, the user is forcefully forgotten.