Currently, to have an extension being notified of artefact installations (such as the autoloader), the extension must provide a fractal interface named "service" and implementing InstallationExtension.
We should make such extensibility point more explicit:
- The ExtensionController should be responsible of giving that information with a method isInstallationExtension() that returns true or false.
- The Fractal component must have an interface implementing InstallationExtension named installationExtension