Remove token and user id keys from session and local storage on logout

Remove 'accessTokenId' and 'currentUserId' keys from session and local storage on logout.
Fixes #61 
Please keep these four lines in the test too, it will serve as a guard for the case if the item names change in the future.

BTW that's why it is better to save an empty value instead of removing the entry. If you keep an empty value, the test will fail if it checks wrong item names.