Increase consistency in src/Developer files

[jhlegarreta]

The files in src/Developer seem to hold some inconsistencies:

• The classes in the ImageFilterX.* and ImageFilterY.* files should probably be renamed to ImageFilterX and ImageFilterY. They currently define a class names ImageFilter, which is also defined in the ImageFilter.* file.
• All files might need to be renamed to have a leading itk*. There are actually some inconsistencies in classes with supposedly similar patterns, e.g. itkImageFilterMultipleInputs.* vs ImageFilterMultipleOutputs.*` -not sure if intended). This will need to be accompanied with the appropriate changes to the include guards.

It is probably a good idea to know if these were intended, and if yes, make it clear the reason, as it does not seem intuitive.

Maybe the notices Warning Fix Errors Example contains errors needed to be fixed for proper output. that are visible in the concerned pages raises from these observations, e.g.
https://itk.org/ITKExamples/src/Core/Common/ProduceImageProgrammatically/Documentation.html

Following #316 (comment).

[dzenanz]

I don't think the inconsistency is intentional. Those examples were contributed by various people, so inconsistency arises naturally. Fixing it would be good.