Nilabels

Requirements are now lower bound to avoid versioning conflicts when installing nilabels within other libraries.

Final name: **NiLabels**.

Closer circle was drawn: external features not strictly related with labels measurements and manipulations had been removed
+ ICV estimation moved in external repository: [intra-cranial-volume-estimation](https://github.com/SebastianoF/intra-cranial-volume-estimation)
+ Dummy generator moved in external repository (was only there for ICV testing): [DummyForMRI](https://github.com/SebastianoF/DummyForMRI)

In progress (in that order)
+ 80% coverage
+ move to python 3 back compatible with python 2.7
+ pip installable
+ integrate in NiPy ecosystem.

First release of labels toolkit for manipulations and measurements of medical image segmentations.