refactor+multi: use *lnwire.FeatureVector for ChannelEdgeInfo features

In this commit, we move the serialisation details of a channel's
features to the DB layer and change the `models` field to instead use a
more useful `*lnwire.FeatureVector` type.

This makes the features easier to work with and moves the serialisation
to where it is actually used.

graph/notifications_test.go

@@ -458,6 +458,7 @@ func TestEdgeUpdateNotification(t *testing.T) {
 			BitcoinSig1Bytes: testSig.Serialize(),
 			BitcoinSig2Bytes: testSig.Serialize(),
 		},
+		Features:      lnwire.EmptyFeatureVector(),
 		ChannelPoint:  *chanPoint,
 		Capacity:      chanValue,
 		FundingScript: fn.Some(script),
@@ -645,6 +646,7 @@ func TestNodeUpdateNotification(t *testing.T) {
 		ChannelID:     chanID.ToUint64(),
 		NodeKey1Bytes: node1.PubKeyBytes,
 		NodeKey2Bytes: node2.PubKeyBytes,
+		Features:      lnwire.EmptyFeatureVector(),
 		AuthProof: &models.ChannelAuthProof{
 			NodeSig1Bytes:    testSig.Serialize(),
 			NodeSig2Bytes:    testSig.Serialize(),
@@ -839,6 +841,7 @@ func TestNotificationCancellation(t *testing.T) {
 			BitcoinSig1Bytes: testSig.Serialize(),
 			BitcoinSig2Bytes: testSig.Serialize(),
 		},
+		Features:      lnwire.EmptyFeatureVector(),
 		ChannelPoint:  *chanPoint,
 		Capacity:      chanValue,
 		FundingScript: fn.Some(script),
@@ -914,6 +917,7 @@ func TestChannelCloseNotification(t *testing.T) {
 			BitcoinSig1Bytes: testSig.Serialize(),
 			BitcoinSig2Bytes: testSig.Serialize(),
 		},
+		Features:      lnwire.EmptyFeatureVector(),
 		ChannelPoint:  *chanUtxo,
 		Capacity:      chanValue,
 		FundingScript: fn.Some(script),