1327 ui update

Description

Change UI according to Rhandros instruction.

First screen (when no account registered) is now Welcome screen instead of AccountSetupBasics (form with mail text input).

Screenshots

Figma with new interface:

https://www.figma.com/file/IYFNR6xuNZXd1hqGl6itT6/02-Mail-app-%F0%9F%94%A8?node-id=1456%3A3865&t=lH68toPk5smqJKsj-4

Technical details

Tests

Issues

e/backlog#1327 (closed)

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