[ENHANCEMENT] Allow filtering by multiple choices at a time in django admin

[mrchrisadams]

Right now, if you're a member of staff, you can filter the admin view based on a single filter at a time, as is normal with django.

However, you often want to filter by more than one at the same time - for example to return all hosting providers marked as 'needs-follow-up' AND 'no-user'.

The library below supports these kinds of queries:

https://github.com/ctxis/django-admin-multiple-choice-list-filter