version 2

[ndem0]

• Move the python-occ to 'cad' submodule: from now on the 'python-occ' package is not mandatory for the installation, but only to access to this submodule. Tests are run according to the environment;
• Refactor the code, merging the parameter classes and the deformation ones (e.g. FFDParameters is encapsulated in FFD);
• Add CustomDeformation (both for CAD or discrete geometries);
• The Handlers classes for CAD are removed;
• The other Handlers are marked as deprecated (will be moved in next releases);
• Improvements in the CAD part, adding features to overcome the known issues.

[ndem0]

@andreamola Please, uncomment all the tests in file tests/test_ffd.py. I suggest to put the additional tests in a new test file.