* Fix#2922 - Load stylesheet from "custom.css" entrypoint when present
This is pretty much the same way it worked as before, albeit with
having to create app/javascript/packs/custom.js with
require('../styles/custom.scss') (or whatever you want really), which
will be a blank slate for you to import whatever you want
* Remove old assets directory
* Extract font-awesome into common.css and always load it
* Create common chunk rather than vendor chunk
vendor chunk is a set of modules provided by external vendors, but now we
can have a chunk as a set of modules shared by multiple entry points,
which could be more efficent than having vendor chunk.
* Start rails-ujs in common.js
This is used by /settings/two_factor_authentication.
