[Cashtab] Add POW to agora landing page

Summary:
We don't really have hard and fast rules about this other than "we do not want many tokens, and the ones that are there should be useful / legit for some reason"

POW makes it

Test Plan: npm test

Reviewers: #bitcoin_abc, Mengerian

Reviewed By: #bitcoin_abc, Mengerian

Differential Revision: https://reviews.bitcoinabc.org/D17794