Check for filter/exclude fields of an object before deciding if to index or delete

[arski]

PR for #8

In particular, I used to have something like qs = self.get_model().objects.filter(foo=1).exclude(related__bar=True) in my model's index's index_queryset method, but this is not being used in queued_search. So this fix makes it possible to define attributes like the following in a model to only index certain objects that pass a filter.

@staticmethod
def queue_filter():
    return {'foo': (1,)}

@staticmethod
def queue_exclude():
    return {'related.bar': (True,)}

[arski]

sad face again