SDIST and WHEEL naming and license cleanup

[jernejfrank]

Minor remarks during the 0.43.0 RC1 release:

1. Produce something like apache_burr-0.43.0.incubating-py3-none-any.whl.
2. Put the correct artifact-specific license in each package under the standard LICENSE name.
3. Add the license declaration to wheel metadata.
4. Ensure the sdist LICENSE only covers dependencies actually shipped in the sdist.
5. Exclude LICENSE-wheel from the sdist.