Switch from PIL to Pillow

Pillow is an actively maintained fork of PIL, can support more image
formats, and has better documentation.
Rotate images based on their EXIF data when saving them.

During saving, Pillow will drop the EXIF data, so we don't need to
worry about clients rotating the images *again* incorrectly
Merge pull request #1199 from maurizi/rotate-image-based-on-exif

Rotate image based on exif orientation