Added HasThumbnail to DulHydra::Models::Base, removed explicit include from Component and Target
Added DulHydra::Error class
Added dul_hydra.rb in lib/ for autoloading
Added DulHydra::ImageDerivative module
Removed thumbnail generation methods from DulHydra::Models::HasThumbnail
Removed thumbnail gemeration tests from shared_examples_for_has_thumbnail
Added unit test module for image derivative tests
Updated test for new thumbnail generation method
Adapted to new thumbnail generation method
Moved files
Code reorganization
Added convenience methods to HasThumbnail for thumbnail generation