Move pytest configuration over to setup.cfg.

This file can house more configurations in one.

django/website/pytest.ini

-[pytest]
-addopts = --reuse-db --strict --tb=short
-python_files=*test.py *tests.py
-norecursedirs = static .ve
-markers =
-    client: marks tests that use the django client (and hence run a bit slow)
-    integration: marks tests that are integration tests (just for noting)
-    groupfactory: marks tests that use the group_permissions methods (and hence run a bit slow)

django/website/setup.cfg

+[tool:pytest]
+addopts = --reuse-db --strict --tb=short
+python_files=*test.py *tests.py
+norecursedirs = static .ve
+markers =
+  client: marks tests that use the django client (and hence run a bit slow)
+  integration: marks tests that are integration tests (just for noting)
+  groupfactory: marks tests that use the group_permissions methods (and hence run a bit slow)