Ticket #48.

This is not finished yet. More work than what I expected but the main part is done.
It will need a lot of testing... There is still a bug when activating a new extension
in development mode (ie. with python web server), I think it does not occur behind
a real web server.

lib/parameters.py

@@ -35,6 +35,12 @@ def register(app, name, type="string", deflt=None, help=None, **kwargs):
     for k, v in kwargs.iteritems():
         _params[app][name][k] = v
 
+def unregister_app(app):
+    if not _params.has_key(app):
+        return False
+    del _params[app]
+    return True
+
 def save(app, name, value):
     if not app in _params.keys() or not name in _params[app].keys():
         raise NotDefined(app, name)