update Create Wallet flow

[decentralistdan]

Why are we doing this?

• A user should be able to get into the wallet within a few seconds and it should not feel like a chore. We would like to postpone having to back up the seed phrase till after a user's wallet receives their first transaction. We also want to remove the security warning screen which is hard to understand for users. (We will add an updated wording to the About screen in the app Settings.)

What are we doing?

• update the tag line on the Zashi Welcome screen

• remove Security Warning screen

• remove seed phrase backup - a user will be prompted to do a backup once they receive their first transaction

What does success look like?

• A user can get from the start screen to the app within a couple of seconds, can immediately start using it, and is not getting frustrated by the need to back up the seed phrase right away.