Restructure wallet storage:

- Perform json deserializations in wallet_db
 - use StoredDict class that keeps tracks of its modifications

electrum/util.py

@@ -280,6 +280,8 @@ class MyEncoder(json.JSONEncoder):
             return obj.isoformat(' ')[:-3]
         if isinstance(obj, set):
             return list(obj)
+        if isinstance(obj, bytes): # for nametuples in lnchannel
+            return obj.hex()
         if hasattr(obj, 'to_json') and callable(obj.to_json):
             return obj.to_json()
         return super(MyEncoder, self).default(obj)