Changes for new NYPL API, incl. multithreaded fetcher (#7773)

Many changes related to new format of data from NYPL.

Added multithreading to fetcher.
- NYPL is currently the only profile for which it's enabled.

Also:
- in couch:  added fetcher_threads to ingestion document
- AbsoluteUrlFetcher.fetch_all_data(): added "set" param.
  - for page numbering in NYPL, IA
- amara.thirdparty.httplib2 has been superceded by
  threadsafe standard library httplib in fetcher
- Fixed handling of type when given a dictionary value