DATACMNS-491 - Add support for configuring null handling hints in Sort.Order.

Null handling hints can now be configured on Order as being either NATIVE (we let the data store decide how to order nulls), NULLS_FIRST or NULLS_LAST.

This is the foundation for custom null-handling in other data store support modules like SD JPA and SD MongoDB.

Original pull request: #79.
DATACMNS-491 - Polishing of null handling API in Sort.Order.

Fixed @since-tags, added author tags where appropriate, fixed copyright header in SortUnitTests. Removed unnecessary formatting line comments. Renamed nullHandlingHint to nullHandling inside Order. Changed builder method signatures to be consistent with with(…) methods defining the direction.

Fixed copy & paste test in SortUnitTests.

Original pull request: #79.