Try to make hud more configurable

Modified files:
* Configuration.py
* HUD_config.xml.example
* HUD_main.py

Instead of tweaking aggregation settings directly in code, make the
values configurable through HUD_config.xml; use the newly created
<hud_ui> element for this. Retain coding convention and key-value
names as they are.

pyfpdb/HUD_main.py

@@ -91,7 +91,7 @@ class HUD_main(object):
         self.db_name = db_name
         self.config = Configuration.Config(file=options.config, dbname=options.dbname)
         self.hud_dict = {}
-        self.hud_params = def_hud_params
+        self.hud_params = self.config.get_hud_ui_parameters()
 
 #    a thread to read stdin
         gobject.threads_init()                       # this is required