attributes not standardized in json_node_export / json-node

[jacobdgm]

The output of json-node in NewCantus currently includes several attributes that are named differently than the corresponding output in the OldCantus's json-node. For example, when querying a Chant in NewCantus, the chant is identified by the id attribute, whereas in OldCantus, the chant is evidently identified by the vid attribute.

Mappings will need to be created to convert the items as they are represented in NewCantus's database into their representation in OldCantus. Separate mappings will likely need to be created for Chant, Sequence, Source and Indexer.