Depend on work_files gem for attachment

[seanupton]

Goal

We need to release, on rubygems.org, an initial work_files gem, which:

• Provides components for work file attachment (primary, derivative) and enumeration/CRUD.
• Is functionally identical to classes that presently reside in lib/newspaper_works/data / NewspaperWorks::Data module, having been ported to an independent gem from there, and maintained in lock-step.

** We then need both of the following:**

1. newspaper_works shall depend on this gem, call its classes, and remove the use of the functionally identical classes in NewspaperWorks::Data.
2. If we move newspaper_works to samvera-labs GitHub, we likely need to move work_files repository there too?

Discussion:

• This is not a high priority, but I suspect this should happen after a 1.0 release.
• We need to set up CI for work_files gem prior to any release.