WIP: Replace band math by functor
This change results from the issue #1671 where the band math filter has been replaced by an itk:NaryFunctorImageFilter. The problem is that the number of required inputs is equal to 2 for this filter but in the app otbBlockMatching.cxx it can be equal to 1. As a result, a pull request has been done to change the number of required inputs in itk:NaryFunctorImageFilter to 1 and we are waiting ITK team.
It is linked to #1671.