[Cashtab] Show timeFirstSeen in tx history

Summary: It's useful to know the time of a tx to higher resolution than 24 hrs. Show this info when a user clicks a tx to expand for more info.

Test Plan: npm start, navigate to tx history screen, click on a tx

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D15161