[Cashtab] Pass chronik as a prop to useWallet hook
Summary:
Pass chronik as a prop to useWallet.js hook. This enables full-app integration testing by passing mock chronik client.
Add a few simple unit tests to confirm this.
Test Plan: npm test
Reviewers: #bitcoin_abc, PiRK
Reviewed By: #bitcoin_abc, PiRK
Differential Revision: https://reviews.bitcoinabc.org/D15381