Add parallel passage references from translations

[KallynGowdy]

Some translations include information about parallel passages. USX also has support for representing this: Reference. They should be represented using the following structure:

type ChapterContent =
    | ChapterHeading
    | ChapterLineBreak
    | ChapterVerse
    | ChapterHebrewSubtitle
    | ChapterParallelPassages;

interface ChapterParallelPassages {
    /**
     * The text content of the parallel passage(s) marker.
     */
    content: string;

    /**
     * The parsed references, if available.
     */
    references?: VerseRef[];
}