Replace navigation buttons for notification details

WordPress/Classes/ViewRelated/Notifications/Controllers/NotificationDetailsViewController.swift

@@ -340,12 +340,20 @@ extension NotificationDetailsViewController {
 
         navigationItem.backBarButtonItem = backButton
 
-        let next = UIButton(type: .custom)
-        next.setImage(.gridicon(.arrowUp), for: .normal)
+        let next = UIButton(type: .system)
+        if let customIcon = UIImage(named: "arrow-up") {
+            next.setImage(customIcon, for: .normal)
+        } else {
+            next.setImage(.gridicon(.arrowUp), for: .normal)
+        }
         next.addTarget(self, action: #selector(nextNotificationWasPressed), for: .touchUpInside)
 
-        let previous = UIButton(type: .custom)
-        previous.setImage(.gridicon(.arrowDown), for: .normal)
+        let previous = UIButton(type: .system)
+        if let customIcon = UIImage(named: "arrow-down") {
+            previous.setImage(customIcon, for: .normal)
+        } else {
+            previous.setImage(.gridicon(.arrowDown), for: .normal)
+        }
         previous.addTarget(self, action: #selector(previousNotificationWasPressed), for: .touchUpInside)
 
         previousNavigationButton = previous

WordPress/Resources/AppImages.xcassets/arrow-down.imageset/Contents.json

@@ -0,0 +1,12 @@
+{
+  "images" : [
+    {
+      "filename" : "arrow-down.pdf",
+      "idiom" : "universal"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

WordPress/Resources/AppImages.xcassets/arrow-up.imageset/Contents.json

@@ -0,0 +1,12 @@
+{
+  "images" : [
+    {
+      "filename" : "arrow-up.pdf",
+      "idiom" : "universal"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}