[Cashtab] notification success & notification error added to Notifications.js

Summary: Related to task: T1768 Breaking notifications into a separate component file.

Test Plan:
cd web/cashtab
npm start
send XEC, ensure notification works
create token, ensure notification works,
send token, ensure notification works
receive XEC, ensure notification works
receive token, ensure notification works,

set error notification to fire on load to view.

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D10360