Correct linter errors, warnings and comments

.pylintrc

data_mining/cli/converter.py

data_mining/cli/harvesters.py

data_mining/datacite/datacite_harvester.py

data_mining/gitlab/__init__.py

data_mining/gitlab/harvest_gitlabs.py

data_mining/sitemap/sitemap_harvester.py

data_mining/unhide_data_model.py

data_mining/util/json_ld_util.py

data_mining/util/json_util.py

data_mining/util/url_util.py

tests/test_datacite_harvester.py

tests/test_harvest_gitlabs.py

tests/test_sitemap_harvester.py

tests/util/test_json_ld_util.py