Qubism - self-similar visualization of many-body wavefunctions 

I am working on visualization schemes for quantum states.
Now it may be not yet merge-ready (I am still working on it), but works.

I was thinking about writing a separate library, but decided it would be better to have in in QuTiP. :)

1. What do you think about it?
2. Should it be in `visualization.py` or in a separate file `qubism.py`?

* J. Rodriguez-Laguna, P. Migdał, M. Ibanez Berganza, M. Lewenstein, G. Sierra,
  Qubism: self-similar visualization of many-body wavefunctions,
  [New J. Phys. 14 053028](http://dx.doi.org/10.1088/1367-2630/14/5/053028) (2012),
  [arXiv:1112.3560](http://arxiv.org/abs/1112.3560)
* Other materials: [poster](http://dx.doi.org/10.6084/m9.figshare.97233),
  [video abstract](http://www.youtube.com/watch?v=tfJHjpyQn0I)
* See also Mathematica and C++ code: https://github.com/stared/qubism.

Examples:

* [AKLT state](https://en.wikipedia.org/wiki/AKLT_Model) (with light colors)
* [Majumdar Ghosh state](https://en.wikipedia.org/wiki/Majumdar-Ghosh_Model) (with dark colors)

![qubism_aklt](https://cloud.githubusercontent.com/assets/1001610/2790141/c65fe630-cbb7-11e3-800e-1466fda4b4ba.png)
![qubism_mg](https://cloud.githubusercontent.com/assets/1001610/2790140/c65d0cc6-cbb7-11e3-8d91-4e4718de0dbb.png)