Include getID3 3rd Party Library License Information

[bpetty]

The getID3 library was added stripped of it's readme.txt referenced in every PHP file that contains the terms of how the library dual-license conditions apply (and why it's perfectly appropriate for distribution with WP).

Typically, I'd suggest the entire distribution was brought in as a vendor library (in a traditional "vendor" folder) completely un-modified, but since WP has already been in the habit of mixing vendor libraries directly in with WP core in various modified ways (and because getID3 is actually incredibly bigger than what was already included), I've only included just the all important license terms that were missing from #23673.

[markjaquith]

In 24203:

Include getID3 licensing info.

props bpetty. fixes #23842.