Simplifying KConfigDialogManager

[David Edmundson]

KConfigDialogManager currently contains a map of every possible widget
along with the name of the signal to connect to to know when a widget
changes.

Can we kill this entire map and replace it with monitoring
widget->metaObject()->userProperty()->notifySignal() at runtime?
It will greatly simplify the code in there, whilst also making it more
extensible/flexible/future proof.

We know that the user property must be set for all the widgets listed
as otherwise they would have to be be listed in the current
s_propertyMap.

If you agree I'll make a patch for review.

David