When a user takes actions while in a high security session, note it on the resulting transactions

Summary:
Ref T13197. See PHI873. Record when a user has MFA'd and add a little icon to the transaction, similar to the exiting "Silent" icon.

For now, this just makes this stuff more auditable. Future changes may add ways to require MFA for certain specific transactions, outside of the ones that already always require MFA (like revealing credentials).

Test Plan:

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13197

Differential Revision: https://secure.phabricator.com/D19665