Use Peer.ID instead of Peer.Key as peer identifier (#664)

Replace Peer.Key as internal identifier with a randomly generated Peer.ID 
in the Management service.
Every group now references peers by ID instead of a public key.
Every route now references peers by ID instead of a public key.
FileStore does store.json file migration on startup by generating Peer.ID and replacing
all Peer.Key identifier references .

management/server/metrics/selfhosted.go

@@ -207,7 +207,7 @@ func (w *Worker) generateProperties() properties {
 				osUIClients[uiOSKey] = osUICount + 1
 			}
 
-			_, connected := connections[peer.Key]
+			_, connected := connections[peer.ID]
 			if connected || peer.Status.LastSeen.After(w.lastRun) {
 				activePeersLastDay++
 				osActiveKey := osKey + "_active"