Fix some Django 1.9 warnings.

mezzanine/generic/fields.py

@@ -3,7 +3,7 @@
 
 from copy import copy
 
-from django.contrib.contenttypes.generic import GenericRelation
+from django.contrib.contenttypes.fields import GenericRelation
 from django.core.exceptions import ImproperlyConfigured, AppRegistryNotReady
 from django.db.models import IntegerField, CharField, FloatField
 from django.db.models.signals import post_save, post_delete

mezzanine/pages/page_processors.py

@@ -2,9 +2,9 @@
 from future.builtins import str as _str
 
 from collections import defaultdict
+from importlib import import_module
 
 from django.apps import apps
-from django.utils.importlib import import_module
 from django.utils.module_loading import module_has_submodule
 
 from mezzanine.pages.models import Page