Delete lunch comments

Cafeteria comments need to be deleted

• frontend placeholder
• backend staging getestet
• backend live (api)

@rapl42 Vorschlag für Backend-Route:
DELETE /cafeteria/comments/$commentId

Backend MR: tc-server!139 (merged)

class DeleteCommentEvent
...
bloc._httpRepo.delete(deleteItemCommentByIdUrl(id));
...
/// URL for deleting CafeteriaItem Comment
String deleteItemCommentByIdUrl(int commentId) =>
    '$cafeteriaBaseUrl/comments/$commentId';