Deletion performance improvement

[luchszebbra]

Description

• Currently datasets cannot be deleted (button is hidden/removed)
• This decision was made because deletion did not work as soon as uploaded media/images was involved (performance/call issues)

The admins need the feature to delete datasets because currently it is not possible to delete wrongly created datasets;

Implementation

The implementation is split up in separate tasks (order)

1. Deletion of dataset deletes deletion constraints #811
2. Delete datasets without deleting images for performance improvement #970
3. Re-implement 'Delete' button for datasets #979
4. Delete images in batches #812