[Cashtab] Show notifications for price milestones

Summary:
Show a notification if we hit a new "tens" place in price, e.g. price goes from sixty-something per 1,000,000 XEC to seventy-something per 1,000,000 XEC

Show a special zero killed notification if price goes over $100 per 1,000,000 XEC

Do not show notifications unless currency is at a similar-ish price basis to USD.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D15912