add drush command

drush.services.yml

@@ -0,0 +1,7 @@
+services:
+  dfg_3dviewer.commands:
+    class: Drupal\dfg_3dviewer\Drush\Commands\Dfg3dViewerCommands
+    arguments:
+      - '@dfg_3dviewer.config_applier'
+    tags:
+      - { name: drush.command }