Build JavaScripts somewhere in this project

[skalee]

Right now every site has its very own package.json. That isn't good, because we can't specify common requirements in one central place. For example, I'd really like to add dependency on Babel's plugin for transpiling Unicode regexps, which is important for us (#135), even though it's now bundled with Babel as one of its default plugins.

Hence, I'm considering building all the required JavaScripts here in this very project. This will make overriding whole scripts more difficult, but perhaps it's not a big deal. Anyway, for maintainability sake, we prefer to configure common scripts rather than override them. Alternatively, maybe this project should produce NPM packages in addition to gems.

I don't know which way to go yet. I'm leaving this ticket open not to forget about this thing, and to open it for discussion.