[Cashtab] Standard component for API error msg

Summary:
T1769

Cashtab API errors were added incrementally in line with other features. The component appears in several screens and should be standardized.

This diff makes the error msg a standard component.

Test Plan:
Edit line 227 of useWallet.js from setApiError(false) to setApiError(true)
npm start
Observe the API error msg on home screen, send screen, settings screen, tokens screen, and send tokens screens; confirm placement and style are ok

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D9984