Streamline Python file headers somewhat

- Add coding statement
  - Import all modules in one line where possible
  - Order: __future__, typing, plain imports, from imports,
    janware modules

Signed-off-by: Jan Lindemann <jan@janware.com>

tools/python/jwutils/Signals.py

@@ -1,5 +1,7 @@
-from abc import ABC, abstractmethod
+# -*- coding: utf-8 -*-
+
 from typing import Dict, Callable
+from abc import ABC, abstractmethod
 
 _handled_signals: Dict[int, Callable] = {}