[ecash-herald] Improve formatting of daily summary msgs

Summary: Add emojis, basic cleanup of the message

Test Plan:
npm test and review before and after screenshot

as-is (msg went out yesterday)

after this diff

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D16931