Consistently refer to members app by English term

I guess it's clear what happened here.

See merge request !3

Implement a committee-based permission system

Warning: this made a mess of the auth system so I have completely new migrations. Just nuke your database and do `./manage.py migrate` (and `createsuperuser` again.)

See merge request !2

Includes tests and an authentication backend to check the permissions
granted to committees.

Remove reference to mongo backend from CI



See merge request !1