Restructure relationship in YAML, XML and JSON formats

[goneall]

Move relationships to a separate array within the document with the format:

        "relationships" : [ {
          "subjectElementId": "SPDXRef-Package"
          "relationshipType" : "DYNAMIC_LINK",
          "comment" : null,
          "objectElementId" : "SPDXRef-Saxon"
        }, {
          "subjectElementId": "SPDXRef-Package"
          "relationshipType" : "CONTAINS",
          "comment" : null,
          "objectElementId" : "SPDXRef-JenaLib"
        },
        . . .
],

Related to SPDX spec issue #96.

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JSON and YAML support is provided by the new SPDX tools library: https://github.com/spdx/Spdx-Java-Library