[Cashtab] [Chronik Websocket Notifications] [Part 4] Unsubscribe to Hash160s when active wallet changes

Summary:
T2447

Depends on D11534

Part 4 of chronik websocket subscriptions for Cashtab

When the user switches active wallets, unsubscribe from previous addresses.

Test Plan:
npm start
Observe subscriptions to hash160s of active wallet
Navigate to settings and change the active wallet
Observe unsubscriptions in the dev console
Send a tx to the new active wallet. Observe a msg in the console.

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D11535