preset: expose new gst.preset_{set,get}_app_dir() on python
preset: expose new gst.preset_{set,get}_app_dir() on python

lubosz/gst-python,pexip/gst-python,alessandrod/gst-python,GStreamer/gst-python,GStreamer/gst-python,alessandrod/gst-python,pexip/gst-python,alessandrod/gst-python,freedesktop-unofficial-mirror/gstreamer__gst-python,freedesktop-unofficial-mirror/gstreamer__gst-python,lubosz/gst-python,pexip/gst-python,lubosz/gst-python,GStreamer/gst-python,freedesktop-unofficial-mirror/gstreamer__gst-python