Add Node Version Manager configuration file and package.json engine
field to clarify Node.js version requirements.

The version of Node.js matters less than the version of NPM in this case
but there's no NVM syntax for NPM version so the Node.js version is
specified everywhere instead as it bundles NPM.

Also, remove package-lock.json until we can support it.

Change-Id: I1ac882ca03cb27721e30031315e034c582e66fe0