Positions filter times out

[jacebrowning]

http://michiganelections.io/api/positions/?election_id=&precinct_id=&precinct_county=Kent&precinct_jurisdiction=City+of+Kentwood&precinct_ward=1&precinct_number=2&active_election=true

[jacebrowning]

Simply filtering by Ward is enough to see the performance issue: http://michiganelections.io/api/positions/?precinct_ward=1&precinct_number=2

[jacebrowning]

The issue seems to be that each additional filter creates a nested JOIN in https://github.com/carltongibson/django-filter. I think I'm going to need help with this one.