Prepare Quorum for Uploads

After this, the server (quorum and participant) should be completely prepared to handle file uploads. There is no proof of storage yet, but I think we can hold off on that until there are actually files in the quorum.

Oh wait, that's not strictly true because the synchronization at the beginning doesn't synchronize files.
unless the elements you're copying over are variable length, this pattern of copy/increment offset is best accomplished `Writer` interface, e.g.:
```go
buf := bytes.NewBuffer(gobUA)
buf.Write([]byte(u.SectorID))
buf.Write([]byte{u.Index, u.Sibling})
buf.Write(u.Signature[:])
...
```