Fixup requires
Ignore 404s in OriginalDownloader
Update exporter to expect SupportingFilePath key
Fix Downloader logic

* Modify alternate paths logic
* Break after first successful potential path is found
* Remove local file on 404 errors
* Output what was downloaded
* Update specs
Modify export query

* Separately output Original and Supporting files based on ReadLevel
* Use LEFT JOINs to get records regardless of attached files
* Take most recent (judging from ID) with non-null subjects