menu: set temporary background graphic

Sources/VLCSidebarController.m

@@ -54,6 +54,7 @@
                                                              leftMenuViewController:[UIViewController new]
                                                             rightMenuViewController:_menuViewController];
     }
+    _sideMenuViewController.backgroundImage = [UIImage imageNamed:@"menu-background"];
 
     return self;
 }

vlc-ios/Images.xcassets/Contents.json

@@ -0,0 +1,6 @@
+{
+  "info" : {
+    "version" : 1,
+    "author" : "xcode"
+  }
+}

vlc-ios/Images.xcassets/menu-background.imageset/Contents.json

@@ -0,0 +1,23 @@
+{
+  "images" : [
+    {
+      "idiom" : "universal",
+      "filename" : "menu-background.png",
+      "scale" : "1x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "menu-background@2x.png",
+      "scale" : "2x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "menu-background@3x.png",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "version" : 1,
+    "author" : "xcode"
+  }
+}