DATAMONGO-1127 - Add support for geoNear queries with distance information.

Prepare issue branch.
DATAMONGO-1127 - Add support for geoNear queries with distance information.

We now support geoNear queries in Aggregations. Exposed GeoNearOperation factory method in Aggregation. Introduced new distanceField property to NearQuery since it is required for geoNear queries in Aggregations.

Original pull request: #261.