Allow datagrids to build their own paginators.
Review Request #7631 — Created Sept. 17, 2015 and submitted
DataGrid subclasses can now override build_paginator() in order to provide their own paginator class, or to process the queryset before handing it to the paginator. This is particularly useful when integrating with Haystack, as some additional work needs to be done to fetch the right items in the queryset before giving it to a paginator.
Unit tests pass.
Used this along with some changes in Splat, which were able to override
and build the paginator itself.