Enable support for Python 3.5 (#1954)

* Switch from Python 3.7 to 3.5 in CI

* fixes

python/simulation.py

@@ -1,6 +1,4 @@
 # -*- coding: utf-8 -*-
-from __future__ import annotations
-
 from typing import Callable, List, Tuple, Union, Optional
 
 import functools
@@ -968,7 +966,7 @@ def __init__(self,
                  geometry_center: Vector3Type = Vector3(),
                  force_all_components: bool = False,
                  split_chunks_evenly: bool = True,
-                 chunk_layout: Optional[str, Simulation, BinaryPartition] = None,
+                 chunk_layout: Optional[str] = None,
                  collect_stats: bool = False):
         """
         All `Simulation` attributes are described in further detail below. In brackets