add lnurl-pay and lightning address support

* bundles all payment identifiers into handle_payment_identifier
* adds lnurl decoding
* adds lightning address decoding

electrum/tests/test_lnurl.py

@@ -0,0 +1,12 @@
+from unittest import TestCase
+
+from electrum import lnurl
+
+
+class TestLnurl(TestCase):
+    def test_decode(self):
+        LNURL = (
+            "LNURL1DP68GURN8GHJ7UM9WFMXJCM99E5K7TELWY7NXENRXVMRGDTZXSENJCM98PJNWXQ96S9"
+        )
+        url = lnurl.decode_lnurl(LNURL)
+        self.assertTrue("https://service.io/?q=3fc3645b439ce8e7", url)