Update UserController.php

Add support for using a callback as redirect route instead of only strings
Update zfcuser.global.php.dist

Added documentation refering to the usage of callback as the login_redirect_route.

Usage example:
'login_redirect_route' => function(\ZfcUser\Entity\UserInterface $user) {
    // Any desired code or logic
    return 'my-custom-process-route';
}
Merge pull request #326 from auterium/master

Callback function support for login redirect route