The share jail needs to have a dedicated id per user

When listing the share jail by ID every user needs to have a dedicated share jail:
- it contains a user individual listing of shares
- in the future shares might be renamed
- for search indexing access permissions are tied to the space (and path), which would not work if there is only one share jail. otherwise all share names would be part of the same space index allowing users to search the names assigned by other users.