GESTrackEffect: add the get_props_hastable virtual method
GESTrackEffect: add the get_props_hastable virtual method

Implements this virtual method for bin described effects.

luisbg/gst-editing-services,freesteph/gst-editing-services,luisbg/gst-editing-services,MathieuDuponchelle/PitiviGes,MathieuDuponchelle/PitiviGes,ahmedammar/platform_external_gst_editing_services,cfoch/ges,freesteph/gst-editing-services,cfoch/ges,MathieuDuponchelle/PitiviGes,volodymyrrudyi/gst-editing-services,freesteph/gst-editing-services,ahmedammar/platform_external_gst_editing_services,volodymyrrudyi/gst-editing-services,pitivi/gst-editing-services,cfoch/gst-editing-services,MathieuDuponchelle/PitiviGes,volodymyrrudyi/gst-editing-services,cfoch/gst-editing-services,cfoch/ges,pitivi/gst-editing-services,cfoch/gst-editing-services,pitivi/gst-editing-services,cfoch/gst-editing-services,cfoch/ges,pitivi/gst-editing-services