Omnium builder port to NodeJS

@gkoberger, this PR introduces a builder written in NodeJS javascript. Since scripts/ add-ons are written in JS, it made sense to me that the the underlying frameworks also take advantage of its ecosystem; state-of-the art CSS minifiers (https://github.com/ded/sqwish) and JS minifiers (https://github.com/mishoo/uglifyjs2).

I hope you like it! I haven't seen any issues using this to build BugzillaJS. I will extend Omnium soon to support worker scripts.