Give folders to all existing services

Step 2 of 2 of shipping folders.

migrations/versions/0254_folders_for_all.py

@@ -0,0 +1,38 @@
+"""
+
+Revision ID: 0254_folders_for_all
+Revises: 0253_set_template_postage
+Create Date: 2019-01-08 13:30:48.694881+00
+
+"""
+from alembic import op
+
+
+revision = '0254_folders_for_all'
+down_revision = '0253_set_template_postage'
+
+
+def upgrade():
+    op.execute("""
+        INSERT INTO
+            service_permissions (service_id, permission, created_at)
+        SELECT
+            id, '{permission}', now()
+        FROM
+            services
+        WHERE
+            NOT EXISTS (
+                SELECT
+                FROM
+                    service_permissions
+                WHERE
+                    service_id = services.id and
+                    permission = '{permission}'
+            )
+    """.format(
+        permission='edit_folders'
+    ))
+
+
+def downgrade():
+    pass