[Cashtab] Patch balance toggle initializing hidden

Summary: Related to T2765. Renamed toggleHideBalance to toggleBalanceVisibility as it better describes the setting's purpose. Initialized toggleBalanceVisibility as true. Updated unit tests to reflect the change to default settings.

Test Plan:
cd web/cashtab && npm start
using a private browser window to ensure default settings
import a wallet
observe that the balance visibility toggle is true, and that the balance is visible
toggle balance visibility off and observe that the setting persists across all screens

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D12404