add user_id as extra parameter of the 'jwt_auth_expire' filter - so we can set a different expiry depending of the user.
fix REVOKE TOKEN buttons; was not working on the current user profile page - now those functions are hooked on 'current_screen' instead of 'init'
new function generate_user_token($user_id) - from code that was within generate_token(); which nows invokes it. Offers a way to generate a token by user_id without the need to pass a username & password.