[WIP] t-SNE

This is an implementation of (non-parametric) t-SNE for visualization. See http://jmlr.org/papers/volume9/vandermaaten08a/vandermaaten08a.pdf for details and here for an example with the digits dataset:

![digits](http://www.informatik.uni-bremen.de/~afabisch/files/digits_p40.png)

I don't know that is interesting for sklearn since it can only transform the training data and can only be used for visualization. That is the reason why it is not fully integrated in sklearn yet. There is at least one reference missing for the trustworthiness score.