Add __str__ for (Package|Distribution)Requirement
As requested in https://gitlab.com/coala/package_manager/issues/53 and originally proposed in and necessary for https://github.com/coala/coala/pull/4002
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
As requested in https://gitlab.com/coala/package_manager/issues/53 and originally proposed in and necessary for https://github.com/coala/coala/pull/4002