Saner redirect location on deletion of incomplete files.
Refactors assignments for DC/MODS/Properties metadata streams into a reusable module.
Fixes a single failing test case.
Moves some complex behavior for MODS setter/getter down into the datastream where it belongs.  Module methods are now oneliners.
Tests now cover newly defined setters and getters in the mods datastream.
Eliminates mods setter helper and its tests.
Metadata_assignment.rb now accounts for the potential existence of a descMetadata stream, which is needed for core files currently and will likely be required more later as we get search working for different sorts of objects.
Adds tests accounting for descMetadata stream inclusion.
Merge pull request #63 from nu-lts/feature/eliminate_duplicate_setter_code

Feature/eliminate duplicate setter code