Setting an event/location to draft noes not change older versions

[timobrembeck]

Describe the Bug

When an event/location is saved as draft, only the latest version is marked as "draft" and older public versions are still delivered via the API

Steps to Reproduce

1. Publish event
2. Change the content and save as draft

Expected Behavior

The event should not be delivered at all - since the status is now "draft"

Actual Behavior

The old published version is delivered

Additional Information

We already solved this for pages (all past versions need to be stored as draft when an event is stored as draft) and also need to fix this for events and pois.
Since changing all past versions to draft also means that users without publishing permissions could un-publish events/locations, we have to repeat the fixes for #1445 for events/locations as well.