Create skeleton for chain notifications

* Goal is to backend agnostic source to chain notifications
* Open channels will communicate with this source to register intent
for critical notifications
* Pending notifications will need to be committed to disk.
* Will also need a journal to ensure no notification is missed
* Later goals include extending this to communicate with 3rd party
outsource services

chainntfs/chainntfs.go

@@ -0,0 +1,12 @@
+package chainntnfs
+
+// TODO(roasbeef): finish
+//  * multiple backends for interface
+//   * btcd - websockets
+//   * core - rpc polling or ZeroMQ
+//   * direct p2p
+//   * random bitcoin API?
+//   * electrum?
+//   * other stuff maybe...
+type ChainNotifier interface {
+}

chainntfs/chainntfs_test.go

@@ -0,0 +1 @@
+package chainntnfs