Add all missing deps for building flatpak

With this flatpak is now possible to build and working

pkgs/flatpak/gstreamer-1.0/gst-libav-stop-caching-codecs.patch

@@ -0,0 +1,30 @@
+From 2c371f17af1695bd42f572d5ccdb837152b8b67a Mon Sep 17 00:00:00 2001
+From: Thomas Coldrick <othko97@gmail.com>
+Date: Thu, 8 Nov 2018 17:46:53 +0000
+Subject: [PATCH] gst-libav-stop-caching-codecs
+
+---
+ ext/libav/gstav.c | 16 ++++++++++++++++
+ 1 file changed, 16 insertions(+)
+
+diff --git a/ext/libav/gstav.c b/ext/libav/gstav.c
+index 2a88230..bfd19a1 100644
+--- a/ext/libav/gstav.c
++++ b/ext/libav/gstav.c
+@@ -155,6 +155,13 @@ plugin_init (GstPlugin * plugin)
+   /* build global ffmpeg param/property info */
+   gst_ffmpeg_cfg_init ();
+ 
++  gst_plugin_add_dependency_simple (plugin, NULL,
++      "/app/lib",
++      "libavcodec.so.58,"
++      "libavformat.so.58,"
++      "libswscale.so.5",
++      GST_PLUGIN_DEPENDENCY_FLAG_NONE);
++
+   gst_ffmpegaudenc_register (plugin);
+   gst_ffmpegvidenc_register (plugin);
+   gst_ffmpegauddec_register (plugin);
+-- 
+2.19.1
+