Expire authentication token upon app restart

[MarcS1975]

I logged into an existing Flatnotes application using my password. All fine and all my docs were shown. Then I noteiced that restarting the container keeps me logged into the website. This shuld not happen. Even deleting the container and the docker image and re-installing an updated Faltnotes image does not require me to log in again. I think these are major security risks. Any change of the underlying system should autmooatically kick the user out and force re-login.