Set the primary image once all pictures are set

2021-09-11 (updated 2021-09-11)

Somehow I can't set the primary image once all pictures are set.
When I press the button Reset the default images all associations are gone and I have to reselect the type for all images.

Indeed, I had to fix it but then I did something else. I'll fix it later.
I actually wanted to remove the concept of primary image, but we'll have to live with it for a while ...

Done. Moved the "primary" option below the image flags.

The final idea is that the primary is the main in-game image (or else the main title, or else the main package).
Although the concept is simple, there are quite a number of fixes to make it work smoothly.