Adding `post_screen` and `link_plates_to_screen`

[erickmartins]

Description

PR implementing the features asked for in issue #36.

Checklist

• Docstrings: done
• unit tests: done for post_screen but not for the link - are we not testing link_datasets_to_project either?
• Flake8 pass

For reviewers

• Check that the PR title is short, concise, and will make sense 1 year later.
• Check that new functions are imported in corresponding __init__.py.

[mellertd]

we probably should write tests for the link functions, but I guess no real need to do it now. I'll take a look at this shortly