[Cashtab] Better testing for Home.js screen

Summary:
Update integration tests for Home screen

Snapshot tests are using bad mocks and not actually testing anything. Add some useful tests.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15203