DATAMONGO-566 - Add support for derived delete-by queries.

Using keywords remove or delete in derived query, or setting @Query(delete=true) removes documents matching the query. If the return type is assignable to Number, the total number of affected documents is returned. In case the return type is collection like the query is executed against the store in first place. All documents included in the resulting collection are deleted in a subsequent call.

Additionally findAllAndRemove(…) methods have been added to MongoTemplate.

Original pull request: #147.
DATAMONGO-566 - Polishing.

Inlined a few methods to reduce the number of indirections. Added a bit of missing JavaDoc here and there. StringBasedMongoQuery now prevents a manually defined query from being marked as both count and delete query.

Polished test cases a little.

Original pull request: #147.