[Scene] Back up keystore & private key

Possiblity to back up either keystore, public key or both

Requirements:

• Make sure that sensitive data is obscured
• Ability to show the obscured sensitive data
• Easy way to copy private key to clipboard
• Easy way to copy keystore to clipboard
• Disclaimer text telling the user that they're responsible for securely backing upp the keystore/private key.
• Disclaimer text should tell the user that backing up the keystore is optional
• Checkmark with copy "Keystore/private key is backed up"
• The CTA-button should be disabled if the user has not met the requirements listed above
• Cancel button returns user to Choose wallet

Design:

Invision: