Set notification email automatically after deleting additional email

[Pytal]

Summary

When an additional email is set as the notification email and is deleted, the deleted email will remain as the notification email

This is unexpected behaviour so we fix this by automatically setting the system email as the notification email on deletion

Additional email as notification email

After deletion

	Screenshot
Before
After

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[artonge]

Would it make sense to do the change on the backend side instead of here?

[skjnldsv]

Would it make sense to do the change on the backend side instead of here?

I agree with Louis @Pytal :)

[blizzz]

also would prefer it on the backend side

[skjnldsv]

Closing this pull request due to lack of recent activity and updates; also seeing the two comments about backend :)