Predicate/Property extractor for Limit Override

[Sytten]

As proposed here: https://github.com/coveo/spillway/pull/17#discussion_r85809990 It would be nice to be able to specify a predicate or another property extractor for a Limit Override. My main concern is how we should deal with multiple predicate/property extractor that match the current query. We also want to be efficient, for that Property Extractor is better since we don't allow the user to specify its own verification, but its also less flexible.