This pull requests implements a token based authentication mechanism, which allows the client to authenticate a user without repeated password entry.
If the "Stay signed in" checkbox inside the login scene is checked, an authentication token is generated by the server and sent to the client, which can later be used instead of the password. The token and the user who requested it are stored inside the last_login.db file which is global to the local database.
If an authentication token is present inside the local database, the client attempts token based authentication upon startup. If that fails, the login scene is displayed as before.
One user can use the same token on multipe devices, as it is reused when requested by a client.
The expiration date of a token defaults to 90 days after its creation, but can be adjusted inside the server.properties file.