`ext/` contains extensions modules to external packages.

This may include helpers and plugins, and configuration of those packages as well.

If a package has several extensions, it is better to create an extension entry
point named by `ext/package.js` which will in turn include all the available
extension packages. However, this might not always be applicable, so feel free
to mix and match, but you should always create a package folder for any
package that contains more than one extension.