Add third-party license information

[vickenty]

Add a NOTICE file to the binary distribution that details license
situation for each subdirectory containing third-party code. This file
should fullfill our obligations when distributing third-party code in
the jar-with-dependencies package.

Provide a more compact overview in THIRDPARTY.md.

Add a script that was used to generate the two files above.

[truthbk]

Thank you for doing this. I'm a bit hesitant to add a python script to the repo, but if there's no tooling (mvn plugin or whatever) we can harness to produce a similar notice, then I guess it's OK.

[vickenty]

Not happy about that too, but I couldn't find anything that would do it for us. There is this maven plugin, but I couldn't get it to do what we need here.