Changed PackageService from memory cache to database. WIP

Gemfile

app/controllers/concerns/downloadable_controller.rb

app/controllers/concerns/sociable_controller.rb

app/controllers/v1/collections_controller.rb

app/controllers/v1/learning_objects_controller.rb

app/models/collection.rb

app/models/concerns/downloadable.rb

app/models/concerns/sociable.rb

app/models/learning_object.rb

app/models/package.rb

app/models/package_item.rb

app/services/package_service/generator.rb

app/services/package_service/link.rb

app/workers/package_worker.rb

config/environments/development.rb

config/initializers/paperclip.rb

config/routes.rb

db/migrate/20170223132327_create_packages.rb

db/migrate/20170223132838_create_package_items.rb

db/migrate/20170223140805_add_attachment_file_to_packages.rb