back to our roots: store vendor files in public/vendor instead of
using CDN, hoping to fix #773 (hoping! will follow up). We can close #755 as a result. We use
require() to min/concat for performance. Note, previously we had "too
many files open" error because we had /vendor tracking git submodules,
which includes all files for those projects - now we're downloading
manually, which gives us minimum required files from each project's
build steps