Closes #106: Rewrite signal handling of deamons to correctly continue signal after handling

tracim/tracim/lib/daemons.py

     def __init__(self):
         self._running_daemons = {}
         add_signal_handler(signal.SIGTERM, self.stop_all)
-        add_signal_handler(signal.SIGINT, self.stop_all)
 
     def run(self, name: str, daemon_class: object, **kwargs) -> None:
         """

tracim/tracim/lib/utils.py

 # -*- coding: utf-8 -*-
-
+import os
 import time
 import signal
 
     raise NotImplementedError()
 
 
-def add_signal_handler(signal_id, handler, execute_before=True) -> None:
+def add_signal_handler(signal_id, handler) -> None:
     """
     Add a callback attached to python signal.
     :param signal_id: signal identifier (eg. signal.SIGTERM)
     :param handler: callback to execute when signal trig
-    :param execute_before: If True, callback is executed before eventual
-    existing callback on given dignal id.
     """
-    previous_handler = signal.getsignal(signal_id)
-
-    def call_callback(*args, **kwargs):
-        if not execute_before and callable(previous_handler):
-            previous_handler(*args, **kwargs)
-
-        handler(*args, **kwargs)
-
-        if execute_before and callable(previous_handler):
-            previous_handler(*args, **kwargs)
+    def _handler(*args, **kwargs):
+        handler()
+        signal.signal(signal_id, signal.SIG_DFL)
+        os.kill(os.getpid(), signal_id)  # Rethrow signal
 
-    signal.signal(signal_id, call_callback)
+    signal.signal(signal_id, _handler)