added override to assign media types by media use

[ajstanley]

Link to Github issue or other discussion

Addresses issue 836

What does this PR do?

Allows definition of media types

What changes were made?

Added and implemented media_type_by_media_use config
(also threw in a parameter to allow harvesting i7 data from a list of PIDS)

How to test / verify this PR?

add this to config if additional fields have been defined. Test files should now be of correct media type

media_type_by_media_use:
  - https://projects.iq.harvard.edu/fits: fits_technical_metadata

additional_files:
 - extracted: http://pcdm.org/use#ExtractedText
 - fits: https://projects.iq.harvard.edu/fits
 - service: http://pcdm.org/use#ServiceFile
 - thumbnail: http://pcdm.org/use#ThumbnailImage

Interested Parties

** @mjordan**

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Checklist

• Before opening this PR, have you opened an issue explaining what you want to to do?
• Have you included some configuration and/or CSV files useful for testing this PR?
• Have you written unit or integration tests if applicable?
• Does the code added in this PR require a version of Python that is higher than the current minimum version?
• If the changes in this PR require an additional Python library, have you included it in setup.py?
• If the changes in this PR add a new configuration option, have you provided a default for when the option is not present in the .yml file?

[mjordan]

@ajstanley would you mind sketching out a new section of the docs at https://mjordan.github.io/islandora_workbench_docs/media_types/ for this new feature?

[ajstanley]

You bet.