Move mail account edition into Account Manager

Summary

Manage mail accounts from the Account Manager

Description

What is the current behavior?

Users have to manage email account within the Mail application

What is the improved behavior?

Mail account management is only possible from Settings > Accounts

• it lists account
• it allows to add a new one
• it allows to remove an account

Modification are reflected within Mail application

What does it bring?

Manage all accounts from the same place

Examples

All other default applications

Documentation to implement UI guidelines available at https://gitlab.e.foundation/internal/wiki/-/wikis/ui/how-to-implement-e-ui-guidelines-in-an-app

Validation