WIP: added LDA and MLP

Hey guys (@amohammadi @onikisins @pkorshunov @ageorge @dgeissbuhler @andre.anjos @sbhatta)

I just added two more classifiers in bob.pad.base.algorithm:

• MLP, which relies on bob.learn.mlp
• LDA, which is a derived class of bob.bio.base.algorithm.LDA

I made them as simple as possible ... there are still stuff missing (i.e. docstrings), but I think it may serve as a nice basis to discuss how algorithms in this package should ideally be implemented.

Let me know what you think !