Refactor organization of interface modules

[pdedumast]

At the moment, pymialsrtk modules are organized into the three interfaces preprocess, postprocess and reconstruction.
Some interfaces do not fall into one of these categories, but are still implemented in one of them.

Interfaces should be refactored into more adapted, meaningful and consistent modules.

For instance (TDB):

1. (intensity) correction module for :

• MialsrtkSliceBySliceN4BiasFieldCorrection,
• BtkNLMDenoising,
• MialsrtkCorrectSliceIntensity,
• etc.

2. registration module for:

• MialsrtkImageReconstruction,
• ComputeAlignmentToReference,
• etc.

3. module for image operation:

• BinarizeImage,
• MaskImage,
• etc.

4. module for image measurements:

• QualityMetrics,
• StacksOrdering,
• etc.