LinkedQL: Schema Format Correction & Missing Steps

[iddan]

Extract correction for the schema file format from #897.

• The schema file holds an array of documents. But for JSON-LD to parse it correctly the array should be a value to @graph property.
• Correct schema file @context format
• Register missing steps
• Parse LinkedQL document properties correctly
• Return JSON-LD documents instead of JSON documents
• Parse ProperyPath correctly

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This change is