Display Private key/Mnemonic onscreen and enable account recovery using private key/mnemonic on Casper Wallet

[ghost]

To recover a lost account in the Signer app, a user must import their account using a .PEM file containing the account secret key.
Casper Wallet will continue to support account import by file if only to accommodate users migrating their accounts to Casper Wallet from Signer. The gold standard for account recovery in a web wallet is to use a HD-based recovery phrase. All users new to Casper Wallet will be prompted to generate such a phrase.

Support for secret phrase via CEP72 was originally planned for legacy Signer. Here are the old tickets for reference, which may help to accelerate investigations around technical design for Casper Wallet:
casper-network/ceps#72
casper-ecosystem/signer#92

Onboarding - Recovery Phrase set up
Design: https://www.figma.com/file/mBlqs6l6I2d3ihX80Mswm4/Casper-Signer?node-id=1838%3A7567
As a Casper Wallet user, during onboarding I can generate a new, unique CEP72 mnemonic recovery phrase for my HD key
As a Casper Wallet user, during onboarding I can click on the obfuscated recovery phrase to reveal the words
As a Casper Wallet user, during onboarding I can click a copy button to copy the recovery phrase to my clipboard for one minute
As a Casper Wallet user, during onboarding when I click the copy button a message appears confirming that the phrase is copied to clipboard
As a Casper Wallet user, during onboarding after seeing my recovery phrase I am prompted to verify that i know the phrase by filling in missing words in the sequence.
As a Casper Wallet user, during onboarding, when prompted to Confirm my secret phrase, the Confirm button is disabled until I fill in all of the missing values in the sequence by clicking on the word tags at the top of the screen.
As a Casper Wallet user, during onboarding if I do not enter the right missing values and I click Confirm I will encounter an error message screen prompting me to start over. Clicking the Start over button takes me back to the Confirm Your Secret Phrase screen.
As a Casper Wallet user who selects the right missing values in the Confirm my Secret Phrase step, clicking Confirm will direct me to a confirmation screen indicating that the secret phrase has been generated successfully: "Your secret phrase is confirmed!"
As a Casper Wallet user who has successfully generated a secret phrase for my wallet I will not be prompted to generate a new secret phrase the next time I log in.

Additionally, Signer 2 should support a secret phrase architecture which easily integrates with Ledger. For example Ledger supports a 24 word secret - Signer 2 should do the same.

Recovery phrase retrieval
As a Casper Wallet user, I can view my secret phrase at any time from the Settings menu by clicking on Backup secret phrase

Recovering your accounts using a recovery phrase
As a Casper Wallet user, during onboarding, if I click the 'I already have a Secret Phrase button' I will be prompted to enter it in an input field.


As a Casper Waller user, during onboarding, if I enter an unrecognized recovery phrase into the input field and click 'Confirm', I will encounter an error screen prompting me to start over. Clicking Start Over will direct me one step back to the Recovery Phrase input screen

[canny]

This issue has been linked to a Canny post: Enable account recovery using private key/mnemonic on the Casper Signer 🎉

[karatnyk]

Moving to 'Done' as successfully implemented.