Get rid of PIL pseudo-stdlib imports

Most noticeably, this adds support for the PIL fork Pillow while keeping
compatibility to legacy PIL (which is unmaintained). Fedora and Arch at
the very least switched their packages over to Pillow. More details:
* https://www.archlinux.org/todo/replace-pil-with-pillow/
* https://fedoraproject.org/wiki/Features/Pillow
Remove file that was moved to horizons.engine

Apparently this was missed in 9a1fbea5 - refs #1945