Full ITK5 Upgrade

[allywarner]

Move away from legacy code.

https://github.com/InsightSoftwareConsortium/ITK/blob/master/Documentation/ITK5MigrationGuide.md#legacy-code-removed

[dcwhite]

Is this one done now or is there more Seg3d code that needs to be upgraded to not use legacy stuff?

[jessdtate]

points to ITK master currently. Should be 5.2 tag, but nonexistent right now. @dzenanz is there a take we can point to?

[dzenanz]

I think tag v5.1.2 should work too, as it contains MinPriorityQueueElementWrapper fix. If not, InsightSoftwareConsortium/ITK@facce8f is what I have in one of the builds.