[KPhotoAlbum] Face detection and face recognition

[Tobias Leupold]

> You should test that libkface version is high enough. Since you require a
> minimum version of the API, it is not enough to make sure that the library
> exist.
I already added this: pkg_check_modules(KFACE libkface>=3.2.0)

I'm going to patch libkface with a simpler training method, cheaping out 
having to implement an own TrainingDataProvider. I'll port my implementation 
to this new function and update the version check (after having bumped the 
libkface API version, too, of course).

You'll see it on github :-)

> It is going to be interesting to test the face recognition with fish and
> sea slug pictures I mainly shoot. I sure hope it will work well there.
> Someone, please donate me 10 more hours per day :D
Well, that's up to the digiKam guys who maintain libkface ... or the OpenCV 
guys ;-)