[ecash-herald] Escape chars in open ascii to prevent tg syntax errors

Summary: Came up in logs from latest failure. Wherever herald is trying to print something as ASCII, we have to make sure we are not printing characters that Telegram will interpret as html. We have a function to do this but we need to implement it.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18632