Fading some algorithms from bob.learn.linear

Hi,

This MR goes in the direction of our medium term goal of getting rid of C++ code from our side. In this MR I will:

• Get rid of PCA (in favor of scikit-learn) (and get rid of the machine of course)
• Get rid of LDA (in favor of scikit-learn)
• Get rid of LogisticRegression (in favor of scikit-learn)
• Get rid of BIC (no one uses it)
• Get rid of GFK (no one uses it, this I've implemented for my thesis)
• Port Whitening to python (the bob.bio.spear is going to use it) (eventually moved to scikit-learn)
• Port WCCN to python (the bob.bio.spear is going to use it) (eventually moved to scikit-learn)

As with the database porting, I'll do it little by little along the weeks. In one day we'll finish it.

Closes #14 #13