Record the mime-type given by fits onto the original file

[jcoyne]

Occasionally the client will upload a file with mime type: "application/octet-stream" even though FITS correctly determines its mime to be "video/webm". Since CurationConcerns and Hydra-Derivatives depend on the original file mime type, we should update the original file with the mime type found by FITS.

We don't want to have this situation:

irb(main):002:0> gf.mime_type
=> "video/webm"
irb(main):003:0> gf.original_file.mime_type
=> "application/octet-stream"

[tpendragon]

Calling @grosscol

[jcoyne]

Blocked by samvera/active_fedora#890

[grosscol]

I had not included mime_type as a default property of characterization.

The mime_type update could be done as a consequence of characterization. The characterization will set properties on the generic file. So the generic file could have a property mime_type that has a different response from the mime_type function of the file it contains. I can see how this could be a problem.

Should attempting to update the content file be done as part of the stock characterization? if the generic file's mime_type property was delegated to the original_file, would calling gf.mime_type="application/new-mime" update the original_file?