Merge branch 'master' into submission

.gitlab-ci.yml

Gemfile.lock

README.md

app/builders/learning_object_builder.rb

app/controllers/v1/learning_objects_controller.rb

app/controllers/v1/search_controller.rb

app/models/collection.rb

app/models/educational_stage.rb

app/models/learning_object.rb

app/models/object_type.rb

app/models/review.rb

app/models/search.rb

app/models/subject.rb

app/models/tag.rb

app/models/user.rb

app/serializers/learning_object_obaa_serializer.rb

app/serializers/learning_object_serializer.rb

app/services/search_service/learning_object.rb

app/workers/dspace_upload_worker.rb

app/workers/thumbnail_generate_worker.rb