Rewrite setup.py from scratch

or rather using https://github.com/pypa/sampleproject. Also disable alias in setup.cfg
Remove setup.py aliases

They only seem to make sense when the doc is hosted on pythonhosted.org
Set version in setup.py
Add missing __init__.py

to make sure tests are included in sdist
Use find_packages and specify a few data packages
Follow PEP 440 for version name

and use nilearn.__version__ in setup.py
Merge pull request #309 from lesteve/fix-setup-py-for-release

Fix setup.py for release