Port to new gtuber lib

Current YouTube code was broken for quite some time. Replace it with
the new Gtuber lib to make this code separate, independent and easier to maintain.

src/prefs.js

@@ -1,6 +1,7 @@
 const { Adw, GObject, Gio, Gst, Gtk } = imports.gi;
 const Debug = imports.src.debug;
 const Misc = imports.src.misc;
+const Gtuber = imports.src.gtuber;
 
 const { debug } = Debug;
 const { settings } = Misc;
@@ -537,6 +538,7 @@ class ClapperPrefsPluginRankingSubpage extends Gtk.Box
 var PrefsWindow = GObject.registerClass({
     GTypeName: 'ClapperPrefsWindow',
     Template: Misc.getResourceUri('ui/preferences-window.ui'),
+    InternalChildren: ['gtuber_group'],
 },
 class ClapperPrefsWindow extends Adw.PreferencesWindow
 {
@@ -546,6 +548,7 @@ class ClapperPrefsWindow extends Adw.PreferencesWindow
             transient_for: window,
         });
 
+        this._gtuber_group.visible = Gtuber.isAvailable;
         this.show();
     }
 });