Integrate BraTS 2017 cascaded anisotropic network code in niftynet / its model zoo

[tvercaut]

This issue supersedes the cmiclab issue #149.

As per the 2017-09-04 meeting discussion, we should thrive at making @taigw BraTS challenger (paper at https://arxiv.org/abs/1709.00382) available on niftynet and list it in the model zoo for "advertisement".

Note that we already have the first stage there:
https://github.com/NifTK/NiftyNetModelZoo/blob/master/anisotropic_nets_brats_challenge_model_zoo.md

While the complete implementation is available externally:
https://github.com/taigw/brats17