Split bower_components into it's own directory

refs #757
This is what makes my above statement a non-issue here (because you are just replacing `bower_components/` with `vendor/`).

I suppose it makes sense to instruct folks to use "bower_components/foo-bar/baz.js" when the file is actually in that directory (it is easier to reason about that way) even though in reality at this stage of processing things have already been consolidated into `vendor/`.