Supports multiple titles/abstracts in different languages

• Updates abstract in Document.json to be an array of objects each tagged with the abstract text and the stated language of the abstract, for cases where the input data have both native-language and translated versions of the abstract
• Updates title in Document.json to be an array (as with abstract)
• Renames the directory containing the schema adsingestschema -> json_schema
• Expanded test cases, including failure cases