New ReactOS Website: Assign banner images to the most recent blog and project-news posts

The theme used for the new website shows lists of blog posts/project-news posts together with a banner image for each post (see e.g. the front page).

As all content has been imported from the old website that doesn't support banner images, the theme currently puts a placeholder banner next to each post.
At least the most recent posts should get a real banner image assigned to improve the website look & feel.