Move score normalization from bob.learn.em to bob.bio.base

Shall we move these functionalities from bob.learn.em to bob.bio.base?? These functionalities are in bob.learn.em for historical reasons.

http://pythonhosted.org/bob.learn.em/py_api.html#bob.learn.em.znorm

http://pythonhosted.org/bob.learn.em/py_api.html#bob.learn.em.tnorm

http://pythonhosted.org/bob.learn.em/py_api.html#bob.learn.em.ztnorm