DATAMONGO-888 - Mapping should be applied to Sort. 

`EntityBackedSortConverter`, as an instance of `SortConverter`, takes care of mapping properties to the according names to be used with mongodb.

Conversion will inspect properties within the backing entity to resolve `id`s and additional mapping information within the `@Field` annotation and apply those to the resulting `DBObject`.

The converter will not touch any properties unknown to the backing entity.

`Query.getSortObject()` has been deprecated and will be removed in a subsequent version.

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Should be applied to both `master` and `1.4.x`.