Stable and updated implementation for newest Meteor versions

This fixes all of the problems with outdated node versions and is tested to work out of the box with a stock Meteorite project.

Furthermore it now fetches the latest Node.JS stable version from https://semver.io/node/resolve?range=stable

You can define somewhat semantic values for the range, like https://semver.io/node/resolve?range=0.11.x

It fetches this value and downloads from the new Heroku repository proxy, which is much faster than using the direct amazon S3 url.

The code is also much cleaner and no longer fetches scons (not required).