Most notably, Meteor now has a full-featured module system of its own, so
meteorhacks:npm and packages/npm-container are no longer necessary, and
you can just use `import` and `export` syntax in your .js files.

For installing/manipulating node_modules and package.json, we recommend
using `meteor npm ...` as a replacement for `npm ...`, to make sure you're
using the same version of `npm` and `node` that Meteor is bundled with.

Note that I also took the liberty of upgrading React-related npm packages
to version ~15.x, which doesn't seem to have broken anything, but might be
worth double-checking in your own environment.