Add methods to be able to use the dialog as a non-modal
dialog showing a list of processes or a modal-dialog
for selecting a process.

Connect double-click to 'Accept' for the modal
case (regression from 2.5).

Change-Id: If05a1c40ee6a41135d943e9919a1250db03eeffb
Reviewed-by: hjk <qthjk@ovi.com>