WIP: [NX-451] first go at a normalized component abstraction

Highlights:
* Opaque types for component and asset ids to avoid overuse of strings (and limit implicit meaning)
* Components can have zero-to-many assets, which could be part of an overall archive or exploded
* API signature contains `Record` type from `nexus-componentmetadata` for general metadata access
* Module is `components/nexus-componentbase` for now, need to find proper location for these types
* Prefer immutable types without set methods, thinking any modification should go through a service?
   Something like `componentService.addAsset(component, asset);` as it should make managing concurrency easier
Note the javadoc mentions the returned metadata a snapshot - imho this is safer/simpler than ensuring any interim changes percolate through to the backing store (which iirc is one of the issues with the old nexus attribute system).