Feature: deal with huge result sets

Created by: geoffharcourt

We have an app with tens of thousands of people in it. There are several records that have a person as an association. On the form page for a model that belongs to a person, trying to populate a select list of people results in the app timing out on Heroku or choking when the JS-enabled select field is loaded with all the possible values.

A widget with a search functionality if the potential result set is larger than 10 or so items would be awesome. Administrate already has a search functionality, so this could piggyback on that API.