htlcswitch: add channel link config

Step №1 in making htlcManager (aka channelLink) testable:
Start use config which will allow as mock/stub external subsystems.

htlcswitch/interfaces.go

@@ -3,10 +3,25 @@ package htlcswitch
 import (
 	"crypto/sha256"
 
+	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/roasbeef/btcd/chaincfg/chainhash"
 	"github.com/roasbeef/btcutil"
 )
 
+// InvoiceDatabase is an interface which represents the persistent subsystem
+// which may search, lookup and settle invoices.
+type InvoiceDatabase interface {
+	// LookupInvoice attempts to look up an invoice according to it's 32
+	// byte payment hash.
+	LookupInvoice(chainhash.Hash) (*channeldb.Invoice, error)
+
+	// SettleInvoice attempts to mark an invoice corresponding to the passed
+	// payment hash as fully settled.
+	SettleInvoice(chainhash.Hash) error
+}
+
 // ChannelLink is an interface which represents the subsystem for managing
 // the incoming htlc requests, applying the changes to the channel, and also
 // propagating/forwarding it to htlc switch.
@@ -66,6 +81,10 @@ type Peer interface {
 	// ID returns the lightning network peer id.
 	ID() [sha256.Size]byte
 
+	// WipeChannel removes the passed channel from all indexes associated
+	// with the peer.
+	WipeChannel(*lnwallet.LightningChannel) error
+
 	// PubKey returns the peer public key.
 	PubKey() []byte