Implement Geodesic flow kernel

Recently I implemented the Geodesic flow kernel algorithm for domain adaptation published initially here Gong, Boqing, et al. "Geodesic flow kernel for unsupervised domain adaptation." Computer Vision and Pattern Recognition (CVPR), 2012 IEEE Conference on. IEEE, 2012. in the package bob.bio.htface.

Moving this to bob.learn.linear can be useful for others.