[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/settings.py

@@ -26,7 +26,7 @@ def list_parse_fallback(v):
 class LNbitsSettings(BaseSettings):
     @classmethod
     def validate(cls, val):
-        if type(val) == str:
+        if isinstance(val, str):
             val = val.split(",") if val else []
         return val