Patch by Anders Holst:

Patch by Anders Holst:
* ConfigElement.addNotifier takes a new optional argument
  immediate_feedback (which is True by default). If True the notifier
  is called whenever an editing key is pressed in the element. When
  False, the notifier is only called when editing is finished, i.e
  the element is deselected or the dialog closed.
* ConfigSet is updated in accordance with Teros suggestion so that
  it behaves like the others and feedback can be given immediately.
* All ConfigElements are modified to check whether they have changed
  since last selected (by a new variable last_value).
* UsageConfig.py is updated to use immediate_feedback=False in the case
  of validating the speeds. (The only case so far where this setting
  is needed, but with the possibility more uses may follow.)