Lossless rotating/flipping of images

[karlch]

The jpegtran tool shows that it is possible to do lossless transformation of images. It would be nice if vimiv did this as well. As we already use a C extension for brightness and co., this might be possible in there as well.

[karlch]

Closing as new features will only be implemented in the Qt port. The follow-up issue can be found here.