We do a `client.load_store()` to restore a previous session.
If both token and password are defined, token is preferred, since it wont create a new device for the bot. One or the other needs to be defined.
Requires https://github.com/anoadragon453/nio-template/pull/20 for the configuration change since password and access token must both be optional (but one must be given).
In the case of `required or not default` with default defaulting to `None` it's impossible to have a `required=False` config item, without supplying a default
To make `required=False` actually mean "you don't need to specify this at all", it needs to be `required and not default` when checking if we should raise `ConfigError`.
