Update the Local Subjects Export Format

[maanasb01]

The feature of exporting the local subjects has been implemented. Linked Issue: #58, Linked PR: #77

Currently, the output format looks like this. it aligns with global Linked Data standards (Schema.org):

{"@context": "https://schema.org/", "@type": "DefinedTerm", "name": "Chemistry, "inDefinedTermSet": "mlk"}
{"@context": "https://schema.org/", "@type": "DefinedTerm", "name": "Agriculture", "inDefinedTermSet": "mlk"}
{"@context": "https://schema.org/", "@type": "DefinedTerm", "name": "Civil Rights", "inDefinedTermSet": "mlk"}

The exported subjects format is to be changed to the RDF format. More details on issue #58.