RavenDB-2800: RavenFS File-Metadata-Etag display in studio

Fixed: We were leaking some headers into the process that should have been effectively removed when creating the metadata object.
Fixed: When the metadata not shown wasn't a primitive object if fail when reconstructing it to be sent. Ex: Raven-Synchronization-History
Fixed: In some places we were still using Last-Modified instead of Raven-Last-Modified