[Cashtab] Replace antd notifications and pop-up modals with react-toastify

Summary:
T2207

Implement a non-antd notification component for Cashtab

Went with react-toastify as

• it looks great
• it is well supported
• it "just works" out of the box, with the same API as antd
• A custom notification component actually is a pretty big job if you want it to look good. No need to reinvent the wheel.

I'm sure toastify will have things I dislike but it won't consume the entire app like antd has.

Test Plan:
npm test

This diff is deployed at https://cashtab-local-dev.netlify.app/

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D15769