move nirvana images to their own directory
oops, img02 should be a png, not a jpeg
add images and attributions for 'trouble' mode

This commit adds images for 'trouble' mode, and adds attributions for
each of the authors in README.md. Each of the images was CC-BY at the
time of download, and was modified from JPEG to PNG and cropped to
1920px by 1080px.
behold! trouble mode, the antithesis of nirvana

By default this feature is disabled. But if a user puts
trouble_threshold in their waylon.yml, trouble mode will be activated if
the number of failed builds is greater than or equal to
trouble_threshold.