POC: [NX-496] Component metadata api

https://issues.sonatype.org/browse/NX-496
I got the sense that some repository formats there will be exactly one, but maven and others, there could be a few (half a dozen at most?). But content of individual wars, no, from what I've read, I don't think we're "exploding" any of the files that are naturally provided as archives by the repository format. 

Basically whatever we want to store as a blob. It strikes me that we don't have to actually store all the maven files in particular as blobs though. Like the digest (.sha1, etc)...can be made to look like files in the view, but don't actually need to map to blobs.

Another thing to consider is mashing all of a component's blob metadata into an UberContentMetadata object. But we'd have to consider the search implications of that (if we throw the metadata into a map or list attribute, AFAICT, we are going to have to give up indexing on the constituent attributes of each blob. Maybe that is ok, but something to think about.