Pull COFFEE out of PyOP2

COFFEE is detached from PyOP2. We also:
* Update the installation instructions
* Update the requirements of PyOP2
* Change the COFFEE's modules names (which were obsolete)

Obviously, as specified in the installation instructions, this introduces a new requirement: COFFEE, available at:
``https://github.com/FabioLuporini/COFFEE/``
This can only be resolved once COFFEE is registered on PyPI. Annoyingly, [someone is sitting on the name](https://pypi.python.org/pypi/coffee/).