Fixes #164

There appears to be quite the mess out there with regard to how DRF
handles filtering.  DRF has its own built-in stuff, but recommends
django_filter for the advanced stuff, which has its own overriding
module that explodes with this message when used as per the
documentation:

  AttributeError: 'NoneType' object has no attribute 'DjangoFilterBackend'

Then there's djangorestframework-filter, another package that claims to
do the same thing, that does everything just differently enough that
nothing worked while I had it enabled.

I ended up using django_filter, but doing so importing each element
explicitly, rather than just using the recommended (and broken, at least
in this project) method of:

    import django_filter.restframework as fitlers

Anyway, this should bring the dependencies up to date, and strips out a
lot of redundant code.

src/paperless/settings.py

@@ -36,7 +36,6 @@ if os.path.exists("/etc/paperless.conf"):
     load_dotenv("/etc/paperless.conf")
 
 
-
 # Application definition
 
 INSTALLED_APPS = [