Change default config to disable Debugbar in CLI

After few hours of struggle :smile:, I've found Debugbar to eat a bit of resources for CLI operations involving large amounts of DB inserts. This is normal, since every log-data uses some memory but unfortunately - quite hard to track down.

This PR adds simple logic for `config.enabled` to prevent Debugbar from CLI mode by default (artisan ...). Just to save someone's time in the future :)

BTW: the `Debugbar::disable();` before seeding loop didn't seem to solve the memory use growth issue, hence this PR.