Changed identifiers for components and events to be URIs.
Prefabs support either the full uri, or just the name portion of a component uri. In the latter case they are resolved within the module and its dependencies (including engine, implicitly).
AssetManager is not longer a singleton, and is instead installed into the CoreRegistry. Tweaked load order to support this.
Various tweaks to serialization to support both the full uri, and resolution when given a partial uri (this keeps the changes backwards-compatible with existing saved games).