[Cashtab] Faster onboarding for new users

Summary:
Improvements to workflow of a new user creating their first wallet.

Before this diff:

• Backup modal has a ton of text, no one reads it, just click through
• When wallet is created, home page is empty. Not clear how to get to your QR code
• Sideshift button but user needs address to use the button before we implement with API

After this diff

• No backup warning modal. Instead, show backup warning on new wallet page.
• Show QR code on new wallet page.
• Do not show sideshift button for now, since it is not useful without the address.

Test Plan:
npm test, npm start, navigate to localhost:3000 in an incognito window and create a new wallet to test the workflow, send a tx and this screen is replaced by tx history

after creating a wallet:

after a tx:

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D15680