Reorganize code so that we can send Multi Part Payments:

- LNWorker is notified about htlc events and creates payment events.
 - LNWorker._pay is a while loop that calls create_routes_from_invoice.
 - create_route_from_invoices should decide whether to split the payment,
   using graph knowledge and feedback from previous attempts (not in this commit)
 - data structures for payment logs are simplified into a single type, HtlcLog

electrum/lnutil.py

@@ -249,52 +249,36 @@ class Outpoint(StoredObject):
         return "{}:{}".format(self.txid, self.output_index)
 
 
-class PaymentAttemptFailureDetails(NamedTuple):
-    sender_idx: Optional[int]
-    failure_msg: 'OnionRoutingFailureMessage'
-    is_blacklisted: bool
-
-
-class PaymentAttemptLog(NamedTuple):
+class HtlcLog(NamedTuple):
     success: bool
+    amount_msat: int
     route: Optional['LNPaymentRoute'] = None
     preimage: Optional[bytes] = None
-    failure_details: Optional[PaymentAttemptFailureDetails] = None
-    exception: Optional[Exception] = None
+    error_bytes: Optional[bytes] = None
+    failure_msg: Optional['OnionRoutingFailureMessage'] = None
+    sender_idx: Optional[int] = None
 
     def formatted_tuple(self):
-        if not self.exception:
-            route = self.route
-            route_str = '%d'%len(route)
-            short_channel_id = None
-            if not self.success:
-                sender_idx = self.failure_details.sender_idx
-                failure_msg = self.failure_details.failure_msg
-                if sender_idx is not None:
-                    try:
-                        short_channel_id = route[sender_idx + 1].short_channel_id
-                    except IndexError:
-                        # payment destination reported error
-                        short_channel_id = _("Destination node")
-                message = failure_msg.code_name()
-            else:
-                short_channel_id = route[-1].short_channel_id
-                message = _('Success')
-            chan_str = str(short_channel_id) if short_channel_id else _("Unknown")
+        route = self.route
+        route_str = '%d'%len(route)
+        short_channel_id = None
+        if not self.success:
+            sender_idx = self.sender_idx
+            failure_msg = self.failure_msg
+            if sender_idx is not None:
+                try:
+                    short_channel_id = route[sender_idx + 1].short_channel_id
+                except IndexError:
+                    # payment destination reported error
+                    short_channel_id = _("Destination node")
+            message = failure_msg.code_name()
         else:
-            route_str = 'None'
-            chan_str = 'N/A'
-            message = str(self.exception)
+            short_channel_id = route[-1].short_channel_id
+            message = _('Success')
+        chan_str = str(short_channel_id) if short_channel_id else _("Unknown")
         return route_str, chan_str, message
 
 
-class BarePaymentAttemptLog(NamedTuple):
-    success: bool
-    preimage: Optional[bytes] = None
-    error_bytes: Optional[bytes] = None
-    failure_message: Optional['OnionRoutingFailureMessage'] = None
-
-
 class LightningError(Exception): pass
 class LightningPeerConnectionClosed(LightningError): pass
 class UnableToDeriveSecret(LightningError): pass