add note, last-used to API tokens

[minrk]

It would be handy to add a note and last-used timestamp to the API tokens table.

This would allow a "tokens" page to show a table of tokens with a note about what they are for (e.g. "single-user server" or "cull-idle script", enabling informed auditing / deletion of tokens, etc.

cf GitHub's tokens page:

[minrk]

We do this now!