DATAGRAPH-1290 - Add case insensitive order support for custom queries

[ihordz]

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[michael-simons]

Nice PR again! Thanks a lot.

[ihordz]

@michael-simons
I've pushed requested changes.
Thank you for review.

[michael-simons]

This is now on master as 1ec70c4 and on 5.2.x as 0bcf9f2. On 5.2.x I rewrote the tests to use Junit 4 asserts, I didn't want to have mixed styles in the class, but that's an oversight on my side.

Your PRs are adding nice value, thank you, @ihordz .