Output separate images for Hematoxylin and Eosin.

This issue is motivated by https://discourse.itk.org/t/itk-error-hematoxylin-and-eosin-are-getting-mixed-up-failed/4767/36

To be determined:
1. Should these images be produced always or only at the user's request? Tentative answer: only if requested. Incrementally they are very little computational effort; however, including them means that three images are produced rather than just one, and that could be a lot of memory.
2. Should the normalized image always be produced, or only the two new optional images if that is what the user requests? Tentative answer: let the user decide. Saving the output memory may be valuable to the user.
3. If the user requests only the two new images, should they be numbered `output[0]` and `output[1]` or, alternatively, `output[1]` and `output[2]`, with the latter case reflecting that the originally supported `output[0]` is missing from this set of output images. Tentative answer is: `output[0]` and `output[1]`.