Make storage API support remote repos

We are trying to use the storage REST API to get a list of all artifacts in a directory of a virtual repo. Unfortunately, part of the virtual repo is a remote repo and the storage API only lists what is in the local cache for the remote repo.

The browse UI will show what is in the remote system but not yet cached with the ">" character. The storage API should match the output of the browse UI and preferably indicate what is not yet cached through an attribute.