ges-uri-clip: Add the possibility to specify an assets directory
ges-uri-clip: Add the possibility to specify an assets directory

through the GES_TESTING_ASSETS_DIRECTORY environment variable.

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