Full diagonal kl method (the first KL method)

@karlnapf 
take a look at this.
Currently I use the log_det in MatrixOperations.cpp.
 I will use some @lambday's work once other things in the implementation are fine.
Note that this is in CStatistics already. This is such a general operation that it should not be in the MatrixOperations class. I know you are waiting for the linalg framework by @lambday but if we put this kind of stuff into Shogun before, it should be at the correct position! Let me know your thoughts on this