Keep origin remote and refs when creating an object pool

For our fast fork feature, we want to be able to clone directly from a pool. This means we need to keep the refs in the pool. Originally we removed the top level refs because we were intending on a "symmetric" design whereby all of the member repositories would be refs under the namespace refs/remotes/repository123/.... But now, we are changing the design so that the pool only cares about the source repository.

addresses #1552 (closed)