Integrate some remote modules into ITK proper

Some remote modules have been in use for a long time, and should be integrated into the main repository (i.e. InsightSoftwareConsortium/ITK). Some examples are InsightSoftwareConsortium/ITKSplitComponents#50 and InsightSoftwareConsortium/ITKFastBilateral#2.

I think there are more, and we should review the complete list. Better candidates are the remote modules with just one or two filters.

Then there are some rarely used/unused ones, such as KitwareMedical/MultipleImageIterator. I think we should deprecate that one, and schedule it for removal in ITK6. Are there any more?

I created a GitHub issue for this. If you have some opinions, please express them either here or (preferably) on GitHub.