Nacho/robust kernel colorized icp

[nachovizzo]

This PR extends PR#2425.

• I've implemented the robust kernel functionality in the ColoredICP pipeline.
• To do so, I had to expose the TransformationEstimationForColoredICP. I'm not sure if this was not part of the API for some reason.
• The new changes are also compatible with existing code(through default parameters)
• The lambda_geomtric parameters is now expose through the TransformationEstimationForColoredICP class.
• The registration_colored_icp function has now the exact same API that registration_icp. With the difference that other TransformationEstimation objects are not accepted. These 2 functions could be merge in the future.

There are still some weight = 1.0; That I did not want to inject an explicit robust kernel there. For now, this completes the other PR in terms of the registration pipelines. More to come!

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[germanros1987]

Here is an overview of what got changed by this pull request:

Clones added
============
- cpp/open3d/pipelines/registration/ColoredICP.h  1
         

See the complete overview on Codacy

[nachovizzo]

@theNded this PR is ready to review. It doesn't add any new functionality, just some changes to the API.
I have also a full implementation of GeneralizedICP that depends on this PR, whenever this gets merged I'll open the gicp PR.

[theNded]

@theNded this PR is ready to review. It doesn't add any new functionality, just some changes to the API.
I have also a full implementation of GeneralizedICP that depends on this PR, whenever this gets merged I'll open the gicp PR.

That is awesome! G-ICP is one key feature we are missing, thanks for your great contribution!

[theNded]

Reviewed 13 of 14 files at r1, 2 of 3 files at r2, 2 of 2 files at r3.
Reviewable status: complete! all files reviewed, all discussions resolved