Allow to process several images (including orphans)

[bittner]

Currently, the image(s) command is designed to process only a single image. We push several images to APPUiO's registry, hence we must run several commands in our pipeline, which is cumbersome, e.g.

  - seiso image history application --delete
  - seiso image orphans application --delete
  - seiso image history postgres --delete
  - seiso image orphans postgres --delete
  - seiso image history redis --delete
  - seiso image orphans redis --delete

More compact would be good

If seiso would take several images as arguments and the orphans as an option this could be greatly simplified, e.g.

  - seiso images --orphans --delete application postgres redis