DATAMONGO-743 - Added DBObjectToStringConverter.

Added a reading converter to dump DBObject instances into a String directly to enable executing queries against MongoDB into a String version of the query result without marshaling the DBObject into a Map first.
DATAMONGO-445 - Allow to skip unnecessary elements in NearQuery.

Added support for skipping elements for NearQuery in MongoTemplate. As mongodb currently (2.4.4) doesn't support he skipping of elements in geoNear-Queries we skip the unnecessary elements ourselves. We use the limit & skip information from the given query or an explicitly passed Pageable.

Original pull request: #64.