Clean setup

[zaccharieramzi]

Right now the setup file and the travis configuration are doing a lot of duplicated things, sometimes in a very dodgy way.

We should clearly list the dependencies in the setup, and in the setup only, with the dependencies clearly put in the right places (for example only numpy and cython are in the setup_require I think).

This will allow us to have a single place to list dependencies, avoid duplication and confusion.

It will also remove the calls to pip in setup.py which might cause issues depending on the pip version.