[DCP-o-matic] New image handling in DCP-o-matic 2.13.61 and above

Hi all, I have switched DCP-o-matic 2.13.61 to use FFmpeg for still-image handling (rather than using ImageMagick). By "still-image" I mean input from a group of TIFF/EXR/whatever files rather than a MP4/ProRes/etc. I'm hopeful this will fix a number of problems; apart from anything else it should preserve resolution in files with more than 8 bits per pixel. I would be very grateful if anybody could test it: particularly those who have had gamma/other troubles with still-image files. Do let us know how you get on. Best, Carl