channeldb: create new channeldb package, update lnwallet to use new API

* Initial draft of brain dump of chandler. Nothing yet set in stone.
* Will most likely move the storage of all structs to a more “column”
oriented approach. Such that, small updates like incrementing the total
satoshi sent don’t result in the entire struct being serialized and
written.
* Some skeleton structs for other possible data we might want to store
are also included.
* Seem valuable to record as much data as possible for record keeping,
visualization, debugging, etc. Will need to set up a time+space+dirty
cache to ensure performance isn’t impacted too much.

channeldb/db.go

@@ -0,0 +1,54 @@
+package channeldb
+
+import (
+	"bytes"
+	"encoding/binary"
+	"sync"
+
+	"github.com/btcsuite/btcwallet/waddrmgr"
+	"github.com/btcsuite/btcwallet/walletdb"
+)
+
+var (
+	endian = binary.BigEndian
+)
+
+var bufPool = &sync.Pool{
+	New: func() interface{} { return new(bytes.Buffer) },
+}
+
+// Store...
+// TODO(roasbeef): CHECKSUMS, REDUNDANCY, etc etc.
+type DB struct {
+	// TODO(roasbeef): caching, etc?
+	addrmgr *waddrmgr.Manager
+
+	namespace walletdb.Namespace
+}
+
+// Wipe...
+func (d *DB) Wipe() error {
+	return d.namespace.Update(func(tx walletdb.Tx) error {
+		rootBucket := tx.RootBucket()
+		// TODO(roasbeef): other buckets
+		return rootBucket.DeleteBucket(openChannelBucket)
+	})
+}
+
+// New...
+// TODO(roasbeef): re-visit this dependancy...
+func New(addrmgr *waddrmgr.Manager, namespace walletdb.Namespace) *DB {
+	// TODO(roasbeef): create buckets if not created?
+	return &DB{addrmgr, namespace}
+}
+
+// Open...
+// TODO(roasbeef): create+open, ditch New, fixes above
+func Open() *DB {
+	return nil
+}
+
+// Create...
+func Create() *DB {
+	return nil
+}