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/``
Once COFFEE is installed this should no longer be necessary, right?