add creator to metadata, enable dictionary update for metadata, raise status for failign request

[pz-max]

This patch includes several minor fixes and additions:

• if the REST API request fails it is more informative to check the status r.raise_for_status() than None
• it is now possible to update the metadata in change_metadata() with a dictionary update which increases flexibility
• we also had to provide a default for the creator=None otherwhise no project could be published