Use "org.videolan.VLC" as the AppStream ID

Close #19335

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

share/vlc.appdata.xml.in.in

 <?xml version="1.0" encoding="UTF-8"?>
-<!-- Copyright 2016 Jean-Baptiste Kempf -->
+<!-- Copyright 2016-2017 Jean-Baptiste Kempf CC-0 -->
 
 <component type="desktop">
-    <id>vlc.desktop</id>
+    <id>org.videolan.vlc</id>
+    <launchable type="desktop-id">vlc.desktop</launchable>
     <metadata_license>CC0-1.0</metadata_license>
     <name>VLC</name>
     <summary>VLC media player, the open-source multimedia player</summary>