Package

Hello!

This is a quite heavy reorganization and cleanup of the code in preparation of packaging pyFBU following these directions:
http://guide.python-distribute.org/creation.html

Main changes:
- move python/-->fbu/ and kept only files relevant for building a pyFBU package.
- moved runpyFBU.py to bin/ (this means it cannot be the name of the virtualenv).
- moved the plot.py script in utils/.
- moved data/ in tests/linearity. It didn't really make sense having it in the main directory.
- moved and added prior related code in the main fbu/ directory
- implemented a dynamic definition of the prior which allow the user to select his favorite.

I haven't fixed the linearity and bump tests accordingly. It should be just a matter of changing a few paths.

I have only tested a single unfolding with runpyFBU.py, so we should check that nothing is broken with the linearity test.