initial commit for fixing video segmentations

[minimal-scouser]

Context

Video segmentations are broken in cornerstone3d. Well sort of. They are working but they are not properly tied to a frame. Rather they persist across frames which is not ideal.

They used to work in 3d 1.0

Changes & Results

I sense that the mappings of derivedImageId and the currentImageId are not proper, and I confirmed that for every imageId, the mapped derivedImageId is same, which is why these labelmaps are being carried forward.

working demo after changes

compressed-video.mp4

Testing

run the videosegmentation example

Checklist

PR

• [] My Pull Request title is descriptive, accurate and follows the
  semantic-release format and guidelines.

Code

• [] My code has been well-documented (function documentation, inline comments,
  etc.)

• [] I have run the yarn build:update-api to update the API documentation, and have
  committed the changes to this PR. (Read more here https://www.cornerstonejs.org/docs/contribute/update-api)

Public Documentation Updates

• [] The documentation page has been updated as necessary for any public API
  additions or removals.

Tested Environment

• [] "OS:
• [] "Node version:
• [] "Browser:

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