Refactor: using ES6 and transpiring to global and CommonJS

this one is the most complex one because it requires grunt to do all the CLDR computations, but other should be easier, will try to do it for the handlebars helpers and see how it goes.

details:

* the new src/ folder (which is included in the npm pkg) will give you access to the modules written in ES6
* the build folder (probably should be renamed to dist) is the browser/server ready-to-use after transpilation
* all the locale-data files are removed, we don't need them, it is just unnecessary complexity
* there is now a single file that you include via npm or bower to use this library

/cc @tilomitra @juandopazo @ericf