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`.

lnrpc/invoicesrpc/addinvoice.go

@@ -18,6 +18,7 @@ import (
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/lightningnetwork/lnd/channeldb"
+	graphdb "github.com/lightningnetwork/lnd/graph/db"
 	"github.com/lightningnetwork/lnd/graph/db/models"
 	"github.com/lightningnetwork/lnd/invoices"
 	"github.com/lightningnetwork/lnd/lntypes"
@@ -75,7 +76,7 @@ type AddInvoiceConfig struct {
 	ChanDB *channeldb.ChannelStateDB
 
 	// Graph holds a reference to the ChannelGraph database.
-	Graph *channeldb.ChannelGraph
+	Graph *graphdb.ChannelGraph
 
 	// GenInvoiceFeatures returns a feature containing feature bits that
 	// should be advertised on freshly generated invoices.

lnrpc/invoicesrpc/config_active.go

@@ -6,6 +6,7 @@ package invoicesrpc
 import (
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/lightningnetwork/lnd/channeldb"
+	graphdb "github.com/lightningnetwork/lnd/graph/db"
 	"github.com/lightningnetwork/lnd/invoices"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/macaroons"
@@ -53,7 +54,7 @@ type Config struct {
 
 	// GraphDB is a global database instance which is needed to access the
 	// channel graph.
-	GraphDB *channeldb.ChannelGraph
+	GraphDB *graphdb.ChannelGraph
 
 	// ChanStateDB is a possibly replicated db instance which contains the
 	// channel state