Add ability to parse JSON metadata

[jeanetteclark]

In order to support schema.org, we need to add a json parser in addition to the XML parser.

It looks like we need to modify XMLDialect:runCheck() so that if the selector looks like jq, use that, otherwise use the existing selectPath . We'll also need to modify the way the class is instantiated so that it correctly identifiers the format of the metadata document InputStream.