Add DeepLabCut project support

[quantumdot]

Description

Add support for DeepLabCut projects (single- and multi-animal projects)

• support for reading DLC annotations and conversion to Labels instance via sleap_io.io.dlc.load_dlc() and sleap_io.io.dlc.dlc_to_labels().
• support conversion of Labels to DLC annotations via sleap_io.io.dlc.write_dlc() and sleap_io.io.dlc.labels_to_dlc()
• support determining if the DLC project is a single-animal or a multi-animal style project via sleap_io.io.dlc.is_multianimal()
• support loading Skeleton data from a DLC project via sleap_io.io.dlc.load_skeletons()
• known issues:
  • Test coverage is missing some lines which are single-animal specific. Need better test data across different project types.
  • DLC does not include edges in their skeleton definitions, so a skeleton with only nodes and no edges is constructed.
  • Video data may not be properly implemented.
    • I think there is no way for us to know a video or image shape without us first loading it.
    • We currently only set the frame index for an annotation to zero. probably we can parse it from the filename?

Types of changes

• Bugfix
• New feature
• Refactor / Code style update (no logical changes)
• Build / CI changes
• Documentation Update
• Other (explain)

Does this address any currently open issues?

[list open issues here]

Outside contributors checklist

• Review the guidelines for contributing to this repository
• Add tests that prove your fix is effective or that your feature works
• Add necessary documentation (if appropriate)

Thank you for contributing to SLEAP-IO!

❤️

[codecov]

Codecov Report

Merging #25 (7e684de) into main (c55f64e) will decrease coverage by 4.53%.
The diff coverage is 70.83%.

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
- Coverage   98.64%   94.11%   -4.54%     
==========================================
  Files          11       12       +1     
  Lines         740      884     +144     
==========================================
+ Hits          730      832     +102     
- Misses         10       52      +42     

Impacted Files	Coverage Δ
sleap_io/io/dlc.py	70.83% <70.83%> (ø)

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[quantumdot]

CI / Tests are failing on python==3.7 it seems due to pickle protocol version mismatch. See related: DeepLabCut/DLCutils#19. Do you have a DLC dataset which works across the python version 3.8 boundary, where pickle version changed from 4 -> 5?

CI / Tests fail on windows python==3.9 due to an import error for pytables. I don't understand why. Some sort of DLL load error .....