Propagating the order of orderable collections for multi-site

[lorenzhirsch]

As of now, having a translated orderable collection means keeping separate orders per site, reordering separately for every localized version of the entry. Thats a lot of work, and prone to inconsistencies for multilingual sites. The most common use case however would be to automatically propagate the order for every localization. Even better: having the option for the order of the collection to be read-only, non-localizable as you can for other fields right now, would be a great feature for usability for end users.