Add missing notify signals for window title and icon changes.

Adds signals for changes to the window title, window icon and window
icon text.

Change-Id: Ia0ddcb94dda2c9ea790edc061d487765024191cd
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>