ScoreHistoryBaseConverter Class

Custom converter class to deserialize the abstract class SquaddingAssignment into one of its Concrete classes. Typeically can rely on the standard JsonConverter that looks at the $type variable to know what Concrete class to deserialize to. However, the value from $type is specific to a Media class, and not BabelFish, so the values don't match. Thus, we need to write our own converter. Recipe comes from https://stackoverflow.com/questions/20995865/deserializing-json-to-abstract-class

public class ScoreHistoryBaseConverter : JsonConverter