Upgrade orchestra middlewares

Refactor to changes introduced on Django 1.10
https://docs.djangoproject.com/en/2.1/topics/http/middleware/#upgrading-pre-django-1-10-style-middleware

orchestra/contrib/orchestration/middlewares.py

@@ -1,15 +1,15 @@
 from threading import local
 
 from django.contrib.admin.models import LogEntry
-from django.urls import resolve
 from django.db import transaction
-from django.db.models.signals import pre_delete, post_save, m2m_changed
+from django.db.models.signals import m2m_changed, post_save, pre_delete
 from django.dispatch import receiver
 from django.http.response import HttpResponseServerError
-
+from django.urls import resolve
+from django.utils.deprecation import MiddlewareMixin
 from orchestra.utils.python import OrderedSet
 
-from . import manager, Operation
+from . import Operation, manager
 from .helpers import message_user
 from .models import BackendLog, BackendOperation
 
@@ -35,7 +35,7 @@ def m2m_collector(sender, *args, **kwargs):
         OperationsMiddleware.collect(Operation.SAVE, **kwargs)
 
 
-class OperationsMiddleware(object):
+class OperationsMiddleware(MiddlewareMixin):
     """
     Stores all the operations derived from save and delete signals and executes them
     at the end of the request/response cycle

orchestra/core/caches.py

@@ -2,7 +2,7 @@ from threading import currentThread
 
 from django.core.cache.backends.dummy import DummyCache
 from django.core.cache.backends.locmem import LocMemCache
-
+from django.utils.deprecation import MiddlewareMixin
 
 _request_cache = {}
 
@@ -25,21 +25,21 @@ def get_request_cache():
         return DummyCache('dummy', {})
 
 
-class RequestCacheMiddleware(object):
+class RequestCacheMiddleware(MiddlewareMixin):
     def process_request(self, request):
         current_thread = currentThread()
         cache = _request_cache.get(current_thread, RequestCache())
         _request_cache[current_thread] = cache
         cache.clear()
-    
+
     def clear_cache(self):
         current_thread = currentThread()
         if currentThread() in _request_cache:
             _request_cache[current_thread].clear()
-    
+
     def process_exception(self, request, exception):
         self.clear_cache()
-    
+
     def process_response(self, request, response):
         self.clear_cache()
         return response