Add events_max_delay setting for qubes-gui-daemon

Allows gubes-gui-daemon event buffering delay to be configured.

qubesadmin/tools/qvm_start_daemon.py

@@ -54,6 +54,7 @@
     ('trayicon_mode', 'str'),
     ('window_background_color', 'str'),
     ('startup_timeout', 'int'),
+    ('events_max_delay', 'int'),
 ]
 
 formatter = logging.Formatter(