Add thirdpartylibs.xml

[mudrd8mz]

It would help to add the https://docs.moodle.org/dev/Plugin_files#thirdpartylibs.xml file into the plugin. Not all the files have their license included in them (such as shared/statistic.js) and because they do not have the standard moodle boilerplate, they are likely to be a 3rd party library.

Declaring and describing all these in the XML file would also help with excluding these files from the moodle coding style checker.