Django 2.0 compat

[jrabbit]

Placeholder issue while I figure out how big this PR will be :)

[Blutude]

Any updates on this?

[jrabbit]

My branch is working but I haven't had the time to make it into a PR

[jrabbit]

https://github.com/jrabbit/Django-facebook/tree/django2 and attempts to make the tests run in https://github.com/jrabbit/Django-facebook/tree/moretools