Add support for setUpTestData in test template

[bmispelon]

Django 1.8 added support for the setUpTestData method which can speed up the execution of tests.

Between the weird capitalization of the method name and the fact that you need to remember to make it a classmethod, it often takes me a few tries to get it running properly.

I think having an empty one in the tempate would be useful and since there's already setUp and tearDown, I think it makes sense to have setUpTestData as well.