Fix image orientation for PIL engine

PIL lib ignored exif, when saving images.
Pillow lib has this behavior fixed, keeping exif is optional.
More info: https://github.com/python-imaging/Pillow/issues/183

After upgrade to Pillow, there was a regression, because sorl started
to save exif data while manually rotating images according exif.
It resulted in wrong thumbnail orientation.

This is now fixed by removing exif on save.