GH-2932: Fix for NodeFmtLib.strNT and added variants for Triple and Quad.

[Aklakan]

GitHub issue resolved #2932

Pull request Description:

• Fixes NodeFmtLib.strNT
• Also adds strNT and strNQ variants for formatting as N-Quads (and N-Triples). It seems that so far there were no reliable util methods to create a single valid NQ string - unless one goes through riot. None of the formatting methods in NodeFmtLib and FmtUtils seem to produce NQ.

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• Tests are included.
• Commits have been squashed to remove intermediate development commit messages.
• Key commit messages start with the issue number (GH-xxxx)

By submitting this pull request, I acknowledge that I am making a contribution to the Apache Software Foundation under the terms and conditions of the Contributor's Agreement.

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See the Apache Jena "Contributing" guide.

[afs]

Thanks!