Updates the department model to assert an 'is_derivation_of' relationship with regards to NuCollection, which may or may not be semantically correct and merits discussion with David/Patrick.  It's worth noting that usage of :has_model twice seemed to introduce odd behavior into the applicaiton.  Also adds a basic factory/test for the Department model.
Delete the extra lib/nu_file.rb, clean up lib/drs/nu_file a bit.
Breaks the disparate grab bag of Sufia functionality required to keep characterization working into its own module under lib/drs/nu_file/characterizable.rb.  Begins the override of characterize_if_changed.
Atomistic Characterization job now runs FITS characterization on the invoking object.
Updates characterizable so that it only pushes a new job if the content of the object has changed.  Woops
Job gets to the point of saving the thumbnail object to the creating master object.
This gets thumbnailification and characterization working for images mostly.  Do not roll back to this commit in the future and expect good things anywhere else.
Eliminate unneeded comment block and make thumbnail one word.
Refactor characterization job test into something more manageable.
Finish up basic tests for creation of image based thumbnails in the characterization job.
More cleanup
Adds a factory for creating pdf objects, also some basic tests asserting pdf thumbnail generation correctness.
Refactors spec into something less ugly.  Removes the error raise on unsupported content objects being passed to the atomistic_characterization thumbnail creation method.
Makes helper functions private (again).  Thumbnails that are updated rather than created should now get tagged with the appropriate metadata, instead of keeping stale information around.
Spec now tests that the job works correctly on update of objects with preexisting thumbnails.
Merge branch 'feature/redo_characterization_and_thumbnails' into develop

Merging in beginning work on thumbnail creation.  Very much WIP.
Adds methods for tagging/untagging a properties datastream as canonical and a boolean method for checking if an object is the canonical representation.
Adds canonization methods to the common assignment helper.
Creation of master object now tags the created object as the canonical representation.
Characterization job now uses canonical? to determine if a content object merits thumbnailification.  Updated content_type factories to tag relevant factories as canon.