Creates a button container, under the video, onto which buttons can be added
This script should not be not be installed directly. It is a library for other scripts to include with the meta directive // @require https://update.greasyfork.org/scripts/9004/44606/YouTube%20-%20Button%20Container%20%28%40require%29.js
addButtonToContainer('A Test Button', function () { alert('Test.'); }, 'test-button');