provide license information at runtime

Because the licenses for most recipes (including p4a itself) require some form of attribution, I added an "open source licenses" page to my (webview/flask) app that shows the license text for p4a, python, flask, etc.

Unfortunately I had to manually search for and copy the license files (and must not forget to add new ones if the - possibly transitive - dependencies change).

It would be great if p4a provided a way to automatically get this information at run time.
I'd be happy to work on a PR for that (when I have the time).

The issue names no files, tests, or entry points; begin by mapping how python-for-android packages p4a and its direct and transitive dependencies. Define what runtime license information should expose and verify that it remains complete when dependencies change.

Written by the indexing model from the issue text.