Convert to ES6 module system

[claudiopro]

This PR modifies tower-of-babel modules to use the ES6 module system. The only relevant hurdle was the use of a named import for babel-core, as it doesn't use export default.

In babel-processor.js:

var babel = require("babel-core");
//...
var transpile = q.fbind(function (contents, filename) {
    var transpiled = babel.transform(contents, {

Becomes:

import {transform} from "babel-core";
//...
var transpile = q.fbind(function (contents, filename) {
    var transpiled = transform(contents, {

[yosuke-furukawa]

@claudiopro
Thank you for contribution. I don't want to use ES6 modules currently.
Because ES6 module is on spec, but the loader is still in progress.
I like ES6 syntax, but I don't want to write ES6 code under discussion.