Code for automatically updating license headers

[stes]

More updates:

• As discussed, reverted the actual changes to the license headers for now
• Added a new tools directory for future developer tools (like pre-commit functions, etc.)

Some updates:

It is not possible to configure various license statements directly in NOTICE.yml. This is also useful in general to have an overview over third partly licenses applicable to the code.

For updating license headers in the whole repository, simply run

python update_license_headers.py

now. Some TODOs:

• Before merging, we need to remove the old docstring license headers. I left them in this PR to more easily compare if the correct licenses was applied everywhere. I can do that once I got that approval.
• It should be decided where to put the update_license_headers.py helper script. Afaik there is not "developer tools" directory right now. The options I can think of are: (1) leave it in the repo root (2) put it in .github or (3) add it to deeplabcut.utils. Opinions?

Original PR description

Prior to this PR, the license headers in the codebase had two issues:

• They were not standardized, and the version information was outdated ("DeepLabCut2.0", etc.)
• They were added to the modules __doc__ variable because
• Potentially maintainers used some automated tool for this, but the correct license header to use was not added to the repo

This PR proposes the following changes:

• Use license headers that are started by # instead of tripe quotes ("""). This avoids a clash between the module docstring and makes it easier to write API docs on module level.
• Update the contribution guide with instructions of how to automatically update the license headers (see below)
• Add license headers to all files in tests/ and examples/
• Updated the header to "DeepLabCut2.0-2.3 Toolbox" (the version info could optionally also be automatically inserted, if desired) DeepLabCut Toolbox
• License header can now be configured in .copyright.tmpl file

The headers can always be updated by running (this can be automated and e.g. be added to a script that also triggers code formatting w/ black, etc):

find deeplabcut tests examples -iname '*.py' -type f \
  -exec licenseheaders -t .copyright.tmpl -f {} \;
licenseheaders -t .copyright.tmpl -f dlc.py

TODO (for maintainers):

• Please check if the info in .copyright.tmpl is accurate/should be updated
• update non-dlc copy right headers accordingly (see review comments)

[stes]

identified some incorrectly updated headers

[stes]

@AlexEMG pls see my changes:

It is not possible to configure various license statements directly in NOTICE.yml. This is also useful in general to have an overview over third partly licenses applicable to the code.

For updating license headers in the whole repository, simply run

python update_license_headers.py

now. Some TODOs:

• Before merging, we need to remove the old docstring license headers. I left them in this PR to more easily compare if the correct licenses was applied everywhere. I can do that once I got that approval.
• It should be decided where to put the update_license_headers.py helper script. Afaik there is not "developer tools" directory right now. The options I can think of are: (1) leave it in the repo root (2) put it in .github or (3) add it to deeplabcut.utils. Opinions?

[MMathisLab]

"It should be decided where to put the update_license_headers.py helper script. Afaik there is not "developer tools" directory right now. The options I can think of are: (1) leave it in the repo root (2) put it in .github or (3) add it to deeplabcut.utils. Opinions?"

• we could make a dev tooling dir?

[stes]

More updates:

• As discussed, reverted the actual changes to the license headers for now
• Added a new tools directory for future developer tools (like pre-commit functions, etc.)

@AlexEMG @MMathisLab

[AlexEMG]

Thanks, @stes!