[Cashtab] Standardize wallet refresh interval

Summary:
This diff standardizes the wallet refresh interval to 60 seconds.
Note: this is the fallback interval, as websocket events processed by processChronikWsMsg will still trigger instant refreshes.

The reasoning for moving away from basing fallback refresh intervals on websocket availability is because if there is no websocket then there is no chronik server either, so no need to distinguish between the two.

Test Plan:
npm test

• grep -r websocketConnectedRefreshInterval src/ with no output
• npm start
• open dev console and observe the Websocket connected, adjusting wallet refresh interval to 60s message upon initial load
• send XEC to this wallet and ensure instant refresh

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D15281