Can't remove images / project icon from a project

[RubenFricke]

Describe the bug
You can't remove an existing project icon or project images from a project.

To Reproduce
Steps to reproduce the behavior:

1. Open swagger
2. Upload 2 files (images)
3. Create a project with a project icon and 2 project images
4. Use the PUT endpoint to remove the project icon and one of the project images
5. Validate that the images are not removed from the project

Expected behavior
Using the PUT endpoint, you should specify a new selection of project images or a project icon. If the client doesn't specify anything for these properties, they should be removed from the project.