[NX-450] Component Sources & Raw Hosted/Proxy Views

JIRA: https://issues.sonatype.org/browse/NX-450
This was originally in the model, then got dropped, but Chris is resurrecting it as part of his component search PR. The type is here to improve the generic signature in https://github.com/sonatype/nexus-oss/pull/750/files#diff-5c2f33b2c6b5e30af9763e455ae7b84eR25 (result of discussions between Michael, Chris, and myself). The details of this type will be fleshed out by Chris' followup PR.