Inconsistent aspect ratio, samples_per_pixel in book 2

[hollasch]

Just before book 2 chapter 8 (Instances), listing 58 (cornell-box-view) we change the aspect ratio to 1.0, which affects all scenes, including the ones that were previously 16:9, breaking them. If we want the ability to change aspect ratios, then the associated image properties will also need to be uniquely specified in each scene's case statement.

Actually, the images don't match the code we have in src, and it looks like samples_per_pixel was bumped from 100 to 400 in listing 54, again changing the results for scenes 1-5. In addition, our source code has this value set to 100. Like the changed & shared aspect_ratio above, if we're going to switch these values per scene, then each case statement needs to be changed to include all information specific to that scene. Either that, or we need to use values common to all scenes.