Add Python API to send reactions (#3762)

python/src/deltachat/hookspec.py

@@ -49,6 +49,10 @@ class PerAccount:
     def ac_outgoing_message(self, message):
         """Called on each outgoing message (both system and "normal")."""
 
+    @account_hookspec
+    def ac_reactions_changed(self, message):
+        """Called when message reactions changed."""
+
     @account_hookspec
     def ac_message_delivered(self, message):
         """Called when an outgoing message has been delivered to SMTP.