Improve handling of lightning payment status:

- Move 'handle_error_code_from_failed_htlc' to channel_db,
and call it from pay_to_route, because it should not be
called when HTLCs are forwarded.
- Replace 'payment_received' and 'payment_status'
callbacks with 'invoice_status' and 'request_status'.
- Show payment error logs in the Qt GUI
- In the invoices list, show paid invoices for which
we still have the log.

electrum/tests/test_lnpeer.py

@@ -18,7 +18,7 @@ from electrum.lnutil import LightningPeerConnectionClosed, RemoteMisbehaving
 from electrum.lnutil import PaymentFailure, LnLocalFeatures
 from electrum.lnrouter import LNPathFinder
 from electrum.channel_db import ChannelDB
-from electrum.lnworker import LNWallet
+from electrum.lnworker import LNWallet, NoPathFound
 from electrum.lnmsg import encode_msg, decode_msg
 from electrum.logging import console_stderr_handler
 from electrum.lnworker import PaymentInfo, RECEIVED, PR_UNPAID
@@ -251,9 +251,8 @@ class TestPeer(ElectrumTestCase):
         # check if a tx (commitment transaction) was broadcasted:
         assert q1.qsize() == 1
 
-        with self.assertRaises(PaymentFailure) as e:
+        with self.assertRaises(NoPathFound) as e:
             run(w1._create_route_from_invoice(decoded_invoice=addr))
-        self.assertEqual(str(e.exception), 'No path found')
 
         peer = w1.peers[route[0].node_id]
         # AssertionError is ok since we shouldn't use old routes, and the