Fix compatibility with Django 2.0

[claudep]

Fixes #239.

[claudep]

Still WIP work.

[coveralls]

Coverage increased (+0.02%) to 89.553% when pulling e4c017e on claudep:issue239 into 82b7398 on dokterbob:master.

[coveralls]

Coverage increased (+0.1%) to 89.667% when pulling 89e13a0 on claudep:issue239 into 82b7398 on dokterbob:master.

[claudep]

Tests look good now.

[dokterbob]

Wonderful work @claudep! Thanks!

Will look at it again some time soon, but so far it looks really great. :)

[dokterbob]

@claudep Have you, by any chance, have been able to manually check/eye the admin?

[claudep]

No, I haven't.

[dokterbob]

Ok. I’ll see if I can find a minute (unless someone else beats me to it, again). ;)