Switch from django-rest-auth to dj-rest-auth

[jgonggrijp]

I looked up the documentation of the former and it said,

Deprecated

Please use https://github.com/iMerica/dj-rest-auth as this project is no longer maintained. Thanks!

So I guess that is what we should do. I'm putting this with the must-haves, because authentication is rather essential.

[JeltevanBoheemen]

Judging from a quick look at the documentation, the endpoints are exactly the same as django-rest-auth. Leads me to think it's probably not too drastic a change. I'll pick this up (updating my other projects at the same time).