Include scaffolding files

This release allows Robo Drupal to manage its own scaffolding files instead of having an external repo, like https://github.com/thinkshout/drupal-integrations do it.

To take advantage of this, add "thinkshout/robo-drupal" to the "allowed-packages" under the "drupal-scaffold" section of your composer.json file. Example below, where the allowed packages already included a couple other things:

          "drupal-scaffold": {
            "allowed-packages": [
                "pantheon-systems/drupal-integrations",
                "thinkshout/drupal-integrations",
                "thinkshout/robo-drupal"
             ]
          }