bugfix: separating the ALREADY_EXIST and DUPLICATED_NAME cases
XmlDataProvider implements addTeacher, addRoom, addSubject
'Open...' uses a ListDialog instead of a WizardDialog to choose the dataprovider
the openWizard extension-point needs a simple jface IWizard instead of our own OpenWizardFactory
add openWizard extension to the xml based plug-in
some compiler warnings fixed
the infrastructure code for Application uses IApplication (from 4.3) instead of IPlatformRunnable (from 3.7)
Merge pull request #6 from bublag/ui-openwizard-extension

'Open...' displays a ListDialog and after that the selected extension's Wizard