Fix ordering of VACUUM options which changed in PG11. Fixes #3836

While we're at it, fix the JSON handling in the maintenance/backup/restore routes.

web/pgadmin/tools/backup/__init__.py

@@ -276,9 +276,7 @@ def create_backup_objects_job(sid):
         None
     """
     if request.form:
-        # Convert ImmutableDict to dict
-        data = dict(request.form)
-        data = json.loads(data['data'][0], encoding='utf-8')
+        data = json.loads(request.form['data'], encoding='utf-8')
     else:
         data = json.loads(request.data, encoding='utf-8')