it translation fix

I'm reviewing the italian translation of the docs, here are some fixes

* Fixed some major translation error and weird expressions
* Fixed inconsistency for Node.js name (sometimes called node, Node, node.js)
* Removed plurals of english terms (as explained [here](http://www.treccani.it/magazine/lingua_italiana/domande_e_risposte/grammatica/grammatica_391.html)
* Rephrased some sentences that were too literal in favor of a more clear translation
* Fixed some unnecessary person change in verbs
* Fixed some typos