Fix for #65046# Open the pop out view from an email with an attached file:=>...

Implementation notes

The Viewer can be opened from an app with floating window, like an e-mail, a task or a contact, in order to view the attachments. This starts the Viewer in overlay mode, no problems so far. But within the Viewer there's an option to open it in pop-out mode. Doing so lets the pop-out Viewer window appear behind the floating window. Bug 65046.

Discussed with Stefan to minimize the floating windows when the Viewer is opened in pop-out mode.