use libjpeg-turbo, use common libs with crengine

Switch libjpeg to libjpeg-turbo: This will give a slight performance
advantage. Also, it will offer us the Turbo-JPEG API, which is a much
simpler approach to render JPEG/JFIF data. This is without
setjmp/longjmp exceptions and will allow for an easy FFI-based pic_jpeg
interface.

Also fix dependencies of our CREngine integration to use the common
build of Freetype, libpng and jpeg (using libjpeg-turbo). This will
mainly make the resulting library smaller, and remove redundant code.

Needs https://github.com/koreader/crengine/pull/3