[Cashtab] Show 10 txs instead of 20 per page

Summary:
Depends on D18681

Now that we have pagination, there is less need to show so many txs per page. I find it difficult to scroll through 20 txs and mentally keep track of the set. With pagination, we can always get the next txs. imo 10 per page is better UX.

Test Plan: npm test, npm start and see only 10 txs

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18682