ENH: Set Seeds as conntainer objects

[blowekamp]

Best practices are to set member variables as object, and not repeat accessor methods in the interface of the owning object e.g. AddSeed, ClearSeed.

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[blowekamp]

@jhlegarreta I was surprised to see SetSeed[12] marked as deprecated in some documentation changes made in #3866. d58bf56

These were the quick changes I made to have the seeds list behave like objects with setter/getters. Further investigation found other region growing filters with similar interfaces:

• ConfidenceConnectedImageFilter
• ConnectedThresholdImageFilter
• NeighborhoodConnectedImageFilter
• VectorConfidenceConnectedImageFilter
  They all have AddSeed, ClearSeeds, methods. Some have the "SetSeed" method marked as deprecated in the doxygen. I didn't see any with a get method for the seed list.

These classes seem to use std::vector to hold the seed lists. Perhaps performance was a reason for this approach? Modern C++ could do something like filter->SetSeedList(std::move(my_list)) where the data could be moved and not copied.

What can be done to improve the interface of these filters and make them more consistent?

[jhlegarreta]

Really sorry @blowekamp, looks like I was confused by the docstring in the implementation file, which documented the method as being deprecated:
d58bf56#diff-9daea1a5d3498baf38e16ef9fd06da89d2f898c4b599a7eb287a76fc3a720accL105
d58bf56#diff-9daea1a5d3498baf38e16ef9fd06da89d2f898c4b599a7eb287a76fc3a720accL137

But after investigation, I now see that the documentation was not updated and the passage left inadvertently in
c005b54

So please, go ahead and update the documentation.

If possible, can the methods be tested, please?

[jhlegarreta]

This should then say SetSeeds2.