Reactivate `ImageProcessing` module.
Clean up `UseDOImageProcessing.cmake`.
Remove support of precompiled header.

This is not an important feature and the support of this is way too
clunky.
Fix `UseDOImageProcessing.cmake` and a few minor things.
Add `PixelTraits` class to `Core` module for Deriche filters.
Use lower_case and underscores naming style and use `PixelTraits`.
Add stub unit tests for Deriche filter.