Derive model, display hints, media type from file_mimetype

[xurizaemon]

Provided the filenames in CSV have meaningful extensions, we should be able to derive the media type (image, video, audio, binary etc), islandora object model, and other details like display hints from the filename.

Additional columns could potentially be used to override this (default hint one way for PDF, but manually set hint for PDFs that need a particular display) to reduce effort in generating import CSVs.

[xurizaemon]

WIP @ https://github.com/xurizaemon/migrate_islandora_csv/tree/mimetype