Adds an EventBus to Gulliver
Adds an EventBus to Gulliver

The EventBus will initially be used to refactor the flow of the
tasks that need to be run when a PWA is saved (metadata,
lighthouse, icons and push notification), but can also be used
on other parts of the project.

GoogleChromeLabs/gulliver,GoogleChromeLabs/gulliver,GoogleChromeLabs/gulliver