[pose-detection]Add skeleton to demo.

[lina128]

This PR adds skeleton to the demo.

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This change is 

[mhays-google]

Reviewed 3 of 3 files at r1.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @pyu10055)

[pyu10055]

Reviewed 3 of 3 files at r1.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @lina128)

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pose-detection/demo/src/camera.js, line 107 at r1 (raw file):

   * Draw the keypoints on the video.
   * @param keypoints A list of keypoints, may be normalized.
   * @param shouldScale If the keypoints are normalized, shouldScale should be

update the param doc, maybe reverse the parameter order of scaleX and scaleY

[lina128]

Reviewed 3 of 3 files at r1.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @lina128)

pose-detection/demo/src/camera.js, line 107 at r1 (raw file):

   * Draw the keypoints on the video.
   * @param keypoints A list of keypoints, may be normalized.
   * @param shouldScale If the keypoints are normalized, shouldScale should be

update the param doc, maybe reverse the parameter order of scaleX and scaleY

Updated in #631