Simplify config read

tracim/tracim/config/app_cfg.py

     """
     from tg import config
     # Don't start daemons if they are disabled
-    if 'disable_daemons' in config and config['disable_daemons']:
+    if config.get('disable_daemons', False):
         return
 
     manager.run('radicale', RadicaleDaemon)