Dev Modules compatibility for Drush 9

Writing global commands has changed, see http://docs.drush.org/en/master/commands/

Also, the Ansible deployment needs to be adjusted such that drupal_post_deploy_tasks call the correct commands and parameters.

Looks like Drush 9 (beta7) is not ready for global commands yet.

The Dev Modules command is now compatible with Drush 9 and we now also remove the links from a Drupal project to global drush commands, because we expect the global Drush commands dirctly in the drush/contrib subfolder.

Until Drupal's packaging supports libraries, see https://www.drupal.org/node/2474007, we also need an explicit project path for each command in the project's root composer.json.

mentioned in commit 31650938

closed