Prevent unpublished events from ending up in the newsletter

Ghost User
2019-08-28T19:20:57+02:00

Closes #905

#### Previous behaviour
Steps to reproduce:

When you create a newsletter and there are unpublished events in the next two weeks they are included in the newsletter.

#### New behaviour
Steps to validate that it works:

Unp...

Closes #905 (closed)

Previous behaviour

Steps to reproduce:

When you create a newsletter and there are unpublished events in the next two weeks they are included in the newsletter.

New behaviour

Steps to validate that it works:

Unpublished events are not be included.