Provide user self-service to change email address

[jandd]

Is your feature request related to a problem? Please describe.

Company names change, people change jobs, there are a lot of reasons for changed email addresses. We should provide a way to change an email address.

Describe the solution you'd like

Allow self service for people that still have access to their old address.

• request change with a new address when logged in
• send confirmation link to the new address
• change email address when confirmation link URL has been visited

Describe alternatives you've considered

Manual changes by an admin after mail to contact address -> does not scale