allow to configure category of parameters

by default, in datafile headers only value, status etc. is stored.
put the sec node devices 'param_category' to 'general' will
put all parameters into the header

commands.py

@@ -135,6 +135,7 @@ def frappy(main=None, stick=None, addons=None):
     - frappy(''): the stick is removed too
     - addons are not changed when not given!
     """
+    all_cfg = {}
     if main is not None:
         all_cfg = frappy_start('main', main)
         if stick is None: