Ignore warnings on pytest summary

Ignore warnings for Django 2.0 (we will need them once we migrate) and
remove external dependencies warnings (there is not too much we can do
here for now).

pytest.ini

@@ -1,3 +1,17 @@
 [pytest]
 addopts = --reuse-db
 python_files = tests.py test_*.py *_tests.py
+filterwarnings =
+    # TODO: this filter has to be removed before migrating to Django
+    # 2.0 and the code has to be upgrade accordingly
+    ignore::django.utils.deprecation.RemovedInDjango20Warning
+
+    # Ignore external dependencies warning deprecations
+    # django-guardian
+    ignore:Shortcut function 'assign'.*:DeprecationWarning
+    # textclassifier
+    ignore:The 'warn' method is deprecated, use 'warning' instead:DeprecationWarning
+    # django-rest-framework
+    ignore:Pagination may yield inconsistent results with an unordered object_list.*:django.core.paginator.UnorderedObjectListWarning
+    # docutils
+    ignore:'U' mode is deprecated:DeprecationWarning