Change the interface of ProgressDialog to be able to specify separately the frame of the dialog and the component that must be used as a reference to display the dialog.

In some cases the frame that is going to display the progress dialog is hidden just after the progress dialog is displayed (this is the case for most of the cases in the control panel).  Depending on the OS, hiding the parent frame implies to hide the progress dialog.  The result is that the progress dialog is also hidden with the parent frame.  However in other cases it is interesting to pass the frame that displays the progress dialog (for instance when we want to have a modal progress dialog this is required).