Improvement DELETE endpoint

[Payback159]

• The endpoints ask for a namespace string (i.e. I also need to know the postfix, which might not be the case).
• So it would be good if e.g. 'Find namespace by name' at least accepts a regex, or the same parameters as 'Create a new namespace' - infix and suffix, that would be cleanest.
• Alternatively 'Deletes a namespace' could have those input parameters and act idempotent, then I wouldn't need the 'Find namespace by name' endpoint.