ges: Add a duration property to GESTimeline
ges: Add a duration property to GESTimeline

API: GESTimeline:duration property

pitivi/gst-editing-services,cfoch/ges,cfoch/gst-editing-services,pitivi/gst-editing-services,cfoch/ges,pitivi/gst-editing-services,cfoch/gst-editing-services,pitivi/gst-editing-services,cfoch/ges,cfoch/gst-editing-services,volodymyrrudyi/gst-editing-services,volodymyrrudyi/gst-editing-services,cfoch/gst-editing-services,cfoch/ges,volodymyrrudyi/gst-editing-services