Support of stacked photos in Spaces

[yellowfisch]

If you add a stack (Raw+Jpeg, Burst) to a space, only the primary photo is added to the space currently. If you then mark another photo from the stack as the main photo, the previous one will be removed from the Space and neither the previous nor the new primary photo is shown there anymore.

Minimum: When a new primary photo of a stack is selected, it should be taken in the same space where the previous primary photo was located.

Better: When a stack is added to a space, all the images in the stack should appear there and be displayed as a stack in the same way as they are in the normal timeline.