Create setup wizard for configuration generation

[TylerConlee]

Instead of requiring a config.toml to start up, if a config.toml isn't present, Slab should start a setup wizard.

The new start up command would be:

./slab -s=<SLACK-TOKEN> -c=<SLACK-CHANNEL-ID>

The setup would then be ran by DMing the Slab app with @slab setup

[TylerConlee]

Resolved in #238