WIP: Add group modules

[axel-grc]

No description provided.

[acoussat]

Thank you very much! However, the tests fail with the following error:

ModuleNotFoundError: No module named 'itk.pctinputprojection_group'

Do we need to include this new file somewhere else?

[axel-grc]

Thank you very much! However, the tests fail with the following error:

ModuleNotFoundError: No module named 'itk.pctinputprojection_group'

Do we need to include this new file somewhere else?

The CMakeLists was not updated to automatically discover application modules, like we did in RTK, so I added this part

[SimonRit]

Add the mechanism with ggo / C++ files.

For projections reader, remove wrt RTK lineint, Boellaard, i0 and idark options