graph/db: version highest chan id

Add a gossip version parameter to HighestChanID in the Store interface
and both KV/SQL implementations. Update callers in the discovery
ChanSeries and server bootstrap code.

discovery/chan_series.go

@@ -73,12 +73,12 @@ type ChannelGraphTimeSeries interface {
 // in-protocol channel range queries to quickly and efficiently synchronize our
 // channel state with all peers.
 type ChanSeries struct {
-	graph *graphdb.ChannelGraph
+	graph *graphdb.VersionedGraph
 }
 
 // NewChanSeries constructs a new ChanSeries backed by a channeldb.ChannelGraph.
 // The returned ChanSeries implements the ChannelGraphTimeSeries interface.
-func NewChanSeries(graph *graphdb.ChannelGraph) *ChanSeries {
+func NewChanSeries(graph *graphdb.VersionedGraph) *ChanSeries {
 	return &ChanSeries{
 		graph: graph,
 	}