Better screen centering of modal dialogs.

[fabvit]

Today I was working with XYPlorer and after some time I had the need to move the XYPlorer window down. So I grabbed it by the title bar and moved down to a point where only the window title and the main menu where visible (close to the windows taskbar).
Then ... I clicked on Help -> Online Support -> Check for Updates... and booom! since the update dialog is a modal one and is centered on the XYPlorer windows, it was not visible, hence I cannot click its buttons either the Ok or the Cancel one.

Centering every modal dialog on the screen instead of the XYPlorer windows would be more appropriate IMHO.