This Pull Request closes#1912 by migrating to a NPM based build, hopefully making it easier to contribute to the Playground.
Also, reduces the number of features of the editor, since most of them were support for other languages or features that don't make sense in a playground environment. This considerably reduces the number of fetched files per page load and the total size of the playground.
This commit selects the production build (instead of development) for the WebAssembly compilation with Webpack, used in our playground. This might make things a bit faster and smaller.
I also took the opportunity to update all the dependencies and the Test262 suite, but unfortunately this doesn't solve #1824.