Add the possibility to build the cldr data to have only one file per locale to download.

This PR add support for the build of cldr data.

Running a build will generate a cldr layer for each locale specified. The system to configure the locales to build is the same than the one used to preload locales at runtime.

The layer will contains all the json files required by `ecma402/impl/load` and the calendar modules will be added to the regular js layer. 

The code in `ecma402/locales.js` is responsible for writing the layers while the code in `ecma402/load.js` is responsible for picking the right layer if one is available.