CMS-1934 Global event CloseWizardPanelEvent should not be needed - replace with other solution
Removed global CloseWizardPanelEvent
Introduced Closeable interface and made WizardPanel closeable.
Made close actions call close on wizardPanel
Moved specific implementation of askUserForSaveChangesBeforeClosing() to WizardPanel, since now SaveBeforeCloseDialog is in the api too.