refactor: move graph related DB code to graph/db from channeldb

This is a pure refactor commit. It moves over all the graph related CRUD
code from `channeldb` to `graph/db`.

subrpcserver_config.go

@@ -12,6 +12,7 @@ import (
 	"github.com/lightningnetwork/lnd/chainreg"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/fn"
+	graphdb "github.com/lightningnetwork/lnd/graph/db"
 	"github.com/lightningnetwork/lnd/htlcswitch"
 	"github.com/lightningnetwork/lnd/invoices"
 	"github.com/lightningnetwork/lnd/lncfg"
@@ -112,7 +113,7 @@ func (s *subRPCServerConfigs) PopulateDependencies(cfg *Config,
 	chanRouter *routing.ChannelRouter,
 	routerBackend *routerrpc.RouterBackend,
 	nodeSigner *netann.NodeSigner,
-	graphDB *channeldb.ChannelGraph,
+	graphDB *graphdb.ChannelGraph,
 	chanStateDB *channeldb.ChannelStateDB,
 	sweeper *sweep.UtxoSweeper,
 	tower *watchtower.Standalone,