biwi kinect head pose database tutorial

[maxpietsch]

Before submitting

• Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

Adds a tutorial for keypoint detection using the biwi head pose dataset RGB images and landmarks from kaggle.

Still very much work in progress but comments and contributions welcome!

PR review

Anyone in the community is free to review the PR once the tests have passed.
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Did you have fun?

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[codecov]

Codecov Report

Merging #128 (0c7d0c3) into main (400dd2a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #128   +/-   ##
=======================================
  Coverage   69.74%   69.74%           
=======================================
  Files           2        2           
  Lines         347      347           
=======================================
  Hits          242      242           
  Misses        105      105           

Flag	Coverage Δ
Linux	69.74% <ø> (ø)
pytest	69.74% <ø> (ø)

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