Updating labels has concurrency issues / is destructive

When labels are added at the same time by different users or processes (GUI or API request) the labels from the latter request will overwrite the previous labels. This seems to be a flaw in the API design because it's only possible to send the full list of labels. It should be possible to just add or remove a collection of labels with a different API request.

Possible Fixes

Add API endpoints which add / remove labels instead of accepting only a complete list of labels.