Serve images through CDN / change uploader class name:

CareerWave returns cdn url in some case. So fix it.
I should submit a PR of course but, I can't be sure which case nor where to fix...

[nit] You can implement this with inheritance

```ruby
def url
  return super unless asset_host && fog_credentials.present? && fog_credentials[:path_style]
  fog_directory.match(/\/(.*)/)
  [asset_host, $1, path].join("/")
end
```