Passphrase - added "looked at secret" transaction.

Summary: Fixes T4376. Only thing I don't like in the current implementation is clicking "Done" doesn't refresh the page so you don't see the viewed secret transaction until you reload. Also made the textarea read-only as when I was playing with this for the first time I assumed I could also edit from the view secret side of things.

Test Plan: Viewed some secrets, saw some transactions.

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T4376

Differential Revision: https://secure.phabricator.com/D8345