Refactor the module

As @dzenanz pointed in #20 , the module needs to be refactored. Some classes seem to be specialized versions of classes that exist in the toolkit (Canny detection filters, morphological filters, etc.), but it should be investigated whether better inheritance can be achieved.

Some minor issues related to the refactoring, or which could be done while refactoring are:
- Separate the class header from the implementation (e.g. see [itk::DescoteauxSheetnessImageFilter](https://github.com/InsightSoftwareConsortium/LesionSizingToolkit/blob/master/include/itkDescoteauxSheetnessImageFilter.h)).
- Provide *Set* / *Get* methods using ITK macros for all ivars.
- Provide some default values for ivars (e.g. see [itk::DescoteauxSheetnessImageFilter](https://github.com/InsightSoftwareConsortium/LesionSizingToolkit/blob/master/include/itkDescoteauxSheetnessImageFilter.h)).
- Provide the implementation for the `PrintSelf` method in cases which is missing or incomplete.

- Prefer initialization lists over assignment.

Start by inventorying the module's classes and comparing the Canny and morphological filters with their ITK toolkit counterparts. Review the existing headers and implementations, using itk::DescoteauxSheetnessImageFilter as the style reference. Done means the inheritance opportunities and listed consistency issues have been addressed across the module.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.