The appearance and disappearance of the group phase section will now be animated.
The animation will have to be adjusted at some point, since currently the height
is hardcoded.
The reason for the library is, that react-bootstrap doesn't support
animations anymore as of
https://github.com/react-bootstrap/react-overlays/issues/146#issuecomment-282036734
Added login and registration api calls to the function pool,
while the application state is persistet through localStorage.
Also (if signed in) the username will be displayed in the
navigation bar of the website.
This allows requests at url '/t/<code>' to be mapped to '/tournament?code=<code>'
and '/t/<code>/fullscreen' to be mapped to '/tournament-fullscreen?code=<code>'.