add ability to report class size in recovery plot

[sjanssen2]

I thought it might be a good idea to give reader a measure for importance of our contig classes. Therefore, the legend labels can now report about the according ratios (note: missed blocks has a different denominator):

[github-actions]

Python linting (black) is failing

To keep the code consistent with lots of contributors, we run automated code consistency checks.
To fix this CI test, please run:

• Install black: pip install black
• Fix formatting errors in your pipeline: black .

Once you push these changes the test should pass, and you can hide this comment 👍

We highly recommend setting up Black in your code editor so that this formatting is done automatically on save. Ask about it on Slack for help!

Thanks again for your contribution!