Implement user email change use case.

Use case should be used in 2 places:

• on cli using symfony command
• on api endpoint using http request

Additional requirements:

• notify external stats system about user email change (service: stats_system)
• notify external marketing system about user email change (service: marketing_system)
• log this change

Useful:

• You can use existing existing User and UserRepository classes in AppBundle\Model namespace
• For testing you can use built in php server