Checking npm-Version on npm-install

Adding a Script at ``preinstall`` (package.json) that runs before npm install begin.

This script checks if the installed npm-version matches with required at packages.json (item engine.npm) - if not (or on error) da detailed error message is printed to console.

ATTENTION: I don't have check this at windows. Should't be a problem - but can someone do a cross-check on Windows?

See: https://github.com/balderdashy/sails/pull/1742 (discussion) for more details