New DatasetExtractor using a DatasetWorker

Depends on workers/base-worker!411 (merged)

Closes #3 (closed), #6 (closed)

.arkindex.yml

@@ -9,16 +9,3 @@ workers:
     type: data-extract
     docker:
       build: Dockerfile
-    user_configuration:
-      train_folder_id:
-        type: string
-        title: ID of the training folder on Arkindex
-        required: true
-      validation_folder_id:
-        type: string
-        title: ID of the validation folder on Arkindex
-        required: true
-      test_folder_id:
-        type: string
-        title: ID of the testing folder on Arkindex
-        required: true