Only send email to user after event was published

[joergrs]

Currently, when an anonymous user submits an event, a confirmation email is send to the provided address.

This can potentially be misused for sending spam emails to random addresses with the platform as a sender.

Improvement:

• Only send the email to the submitter once the event was confirmed
• Keep sending emails to the editors as soon as the event is submitted

Nice-to-have:

• Give editors the possibility to directly reply from the platform. E.g., to give feedback to the submitter about why his event was rejected.