Give warning or hide download button

[luceos]

Instead of doing only a backend side authentication against the permissions, throw a warning or hide the download button completely in the frontend ux.

[evalation]

This would be great! Currently if a user doesn't have permission to download a file he'll get a JSON error message: {"errors":[{"status":"401","code":"permission_denied"}]}. Either hide the download button or prompt with a login to download dialog.

[clarkwinkelmann]

#194 adds a alert with an unauthorized message. It might still not be the most user-friendly option but that's one step forward.