improve reporting of check_annotations

See https://github.com/IDR/SubmissionWorkflow/pull/29#discussion_r489350914

check_annotations.py script atm is expecting 1-to-1 relationship between images and annotations.
More granular options such as supressing output of the additional entries (i.e. entries which do not match the 1-1 expectation) should be considered

cc @sbesson 