[Cashtab] Reduce tx history rendering

Summary:
Sync methods used to parse tx history are causing slow load times due to newly introduced methods to parse agora txs.

This is not the "right" solution. However there are many parts to the right solution and it could take some time to get into prod.

For now, reduce the number of displayed txs to improve performance while working on the right solution.

Test Plan:
npm test

this is live at https://cashtab-local-dev.netlify.app/#/

it does not really solve the problem. It does noticeably speed up load times for wallets with agora txs in history, tho need to wait for the wallet to load tx history from chronik to get 10 instead of the 20 that will be cached. The speed issue comes from processing the 20 -- we need to cache them better, load and parse async.

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D17309