[Cashtab] Bump rendered txs in history from 10 to 20

Summary:
This is where we were at before discovered / patched the UI-locking slow parsing bug

Going forward will look to implement lazy loading, scrollable history. But for now just get those txs back.

Test Plan: npm test

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D17372