Add language and multi user collaboration support to onlyoffice

[vigonotion]

This PR adds translation support to the onlyoffice editor by extracting the user language from the Accept-Lang header.

It also adds support for multi-user collaborative editing by removing the user id from the key for the onlyoffice document. I understand why you added that in, but I can't think of a case where the key has a hash collision with another totally different file because you already add the HashStream to the key. And in most cases, the user id is also already part of the path, so I'm pretty sure this is okay and enables users to use collaborative editing.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[vigonotion]

This is not stale, waiting for review from @mickael-kerjean

[mickael-kerjean]

This PR has been staying idle for a while already. If the issues aren't fixed I will be closing in the next 2-3 months

[vigonotion]

Sorry, completely forgot about this one. What do you think about the removal of the user id? It is necessary because otherwise multiple users cannot work together.

I will fix the potential runtime error

[rinkp]

While some backends may return different files for different users (e.g. \fileserver\home) with the same path, perhaps a setting per backend would be nice to indicate that files are the same for all users if they can see a certain file. I think adding this would be a useful feature