Large refactoring/feature commit

1. Change listen addresses to URIs
2. Break out connectionSvc to support listeners and dialers based on schema
3. Add relay announcement and lookups part of discovery service

lib/discover/client.go

@@ -43,7 +43,7 @@ func New(addr string, pkt *Announce) (Client, error) {
 }
 
 type Client interface {
-	Lookup(device protocol.DeviceID) []string
+	Lookup(device protocol.DeviceID) (Announce, error)
 	StatusOK() bool
 	Address() string
 	Stop()