[CHORE] flake8 issues E402, E721 and F821 (#1874)

* F821: undefine name
disabled and logged webhook_listener for opennode and lnpay because they are obviously not working
* E402: module level import not at top of file
* E721 fixes, only popped up for python3.9 not 3.10

lnbits/tasks.py

@@ -46,8 +46,8 @@ class SseListenersDict(dict):
         self.name = name or f"sse_listener_{str(uuid.uuid4())[:8]}"
 
     def __setitem__(self, key, value):
-        assert type(key) == str, f"{key} is not a string"
-        assert type(value) == asyncio.Queue, f"{value} is not an asyncio.Queue"
+        assert isinstance(key, str), f"{key} is not a string"
+        assert isinstance(value, asyncio.Queue), f"{value} is not an asyncio.Queue"
         logger.trace(f"sse: adding listener {key} to {self.name}. len = {len(self)+1}")
         return super().__setitem__(key, value)