Unlink achievement visibility from namespace visibility

Achievements can only be seen when the user can see the namespace, where they are created.

This can lead to cases where a user owns an achievement, but can't see it because they are not a member of the namespace which awarded the achievement to them.

An easy solution would be to prevent private namespaces from awarding achievements to non-members.

Open Questions

• What if a public namespace awards achievements and then changes to private?
• What if a private namespace awards achievements to members and these members are removed from the namespace?

Proposal

Allow read_achievement regardless of the namespace visibility. Build in a check for the awarding namespace visibility:

• Display the name of the namespace, if it is public

  

• Display a placeholder for referring to a private namespace: Awarded [XX] ago by private namespace