Improve token usage for users

We want to enable a user to have multiple login tokens simulatenously. A limit should be enforced globally and be editable via the gosdn config file to prevent the creation of unlimited tokens. As token will be invalid after 24h anyways, I suggest 100 tokens at the same time. If the limit is exceeded, the token which was used the most time ago should be overwritten. After each start of gosdn, all tokens older than the validation period should be removed for each user.