Rework logic when to show and enable which action

Show "Restore printed backup" for all (sub)keys and "Export OpenSSH key"
for all authentication subkeys (even if it makes little sense for the
public keys of somebody else, it does make sense for an own public key).
Show the other actions only for own keys. Always showing all actions
for own (sub)keys makes the actions more discoverable.

Disable actions that cannot be used (e.g. because they require access to
the secret subkey) or that make little sense (e.g. restoring a printed
backup if the secret subkey is stored in the key ring).

• GnuPG-bug-id: T6214