Put in place a build system

[ymeine]

To release the product, a build step seems essential: for sub parts building, validation/tests, optimization, packaging, etc...

Several build tools exist, one of the most famous in the JavaScript world being gruntjs (even if it's a more general purpose tool, aimed at executing tasks), but we might maybe choose another system, for even more than build: build and deployment

Once again, a npm script like npm build is welcome.