Add action for refreshing (multiple) keys to key list

As part of this, the RefreshCertificateDialog is adapted to refreshing multiple keys.
Showing correct results for this proved tricky - both in implementation and UX,
as there are many potential outcomes. The intended UX is roughly:

• If only one key is refreshed, the command should behave as it did previously
• If multiple keys are refreshed, errors are shown, while also showing if the "other"

job (smime or pgp) has succeeded.

• If multiple keys are refreshed, exact information like "key was not found" and "key was not changed"

is not shown.

• GnuPG-Bug-ID: T6739