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.

requirements.txt

@@ -1,10 +1,9 @@
-Django==1.10.3
+Django==1.10.4
 Pillow>=3.1.1
 django-crispy-forms>=1.6.0
 django-extensions>=1.6.1
-django-filter>=0.12.0,<1.0
+django-filter>=1.0
 djangorestframework>=3.4.4
-djangorestframework-filters>=0.8.0
 filemagic>=1.6
 langdetect>=1.0.5
 pyocr>=0.3.1