Investigate annotations and decide on annotation format

[ilgazer]

As per customer requests, we need to be able to annotate requests, needs, actions etc. As a part of this, we will need to decide what annotation fields we will use. The product of this issue will guide the work in #541 and #542

[ilgazer]

I settled on the following annotation format. The nested selectors allow us to efficiently fetch only the annotations for the resources/needs/warnings we have.

    {
        "@context": "http://www.w3.org/ns/anno.jsonld",
        "id": "http://example.org/anno1",
        "type": "Annotation",
        "bodyValue": "This is no longer true, as we have recently discovered.",
        "target": {
            "source": "http://example.org/page1.html",
            "selector": {
                "type": "XPathSelector",
                "value": "//div[@id=\"Resource1\"]",
                "refinedBy": {
                    "type": "RangeSelector",
                    "startSelector": {"type": "XPathSelector", "value": "/p[1]"},
                    "endSelector": {"type": "XPathSelector", "value": "/p[1]"},
                    "refinedBy": {"type": "TextPositionSelector", "start": 1, "end": 29}
                }
            }
        }
    }