Improvements for statismo python wrapper module

[normanius]

On MacOS, when building the wrapper, I end up with two files _statismo_VTK.so and statismo_VTK.py under build/modules/VTK/wrapping.

What I currently do to use the python wrapper is the following:

• Create a folder statismo or statismo_VTK under my python's module directory (.../lib/python2.7/site-packages/statismo)
• Copy _statismo_VTK.so and statismo_VTK.py to that location
• Create an __init__.py file with the following line (from statismo_VTK.py import *)

This way I can import the statismo library and all is good.

For better usage, I'd suggest however the following improvements:

• cmake installation target to bundle the relevant files into a python module statismo
• because it always is a hassle an extra entry: fix dependencies for installed binaries in cmake
• Just a matter of preference: try to hide the ugly _vtk and _vtkPD postfixes by either one of the suggestions:
  • Create a new namespace/submodule vtk where it is clear that only vtkPolyData stuff is used. One would use that module as something like import statismo.vtk as statismo
  • Similar as for vtkStandardMeshRepresenter, just prefix all statismo objects created for vtk with vtk*, a prefix a vtk users are pretty familiar with
  • Just entirely skip it, unless there is the plan to further expand to other container types
  • Hide the specializations by using some data managing layer when creating the object, for instance

    if isinstance(representer, vtkStandardMeshRepresenter): 
        return statismo.DataManager_vtkPD.Create(representer)

Not sure if I have time to fix this myself, just making suggestions which I would pick up in case I continue to work with statismo for bit... :)