Reuse the IOS code for WAD installation

* Less code and logic duplication.

* Fixes a bug with the data dir not being created, steps being done in
  the wrong order.

Source/Core/UICommon/WiiUtils.h

@@ -0,0 +1,14 @@
+// Copyright 2017 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <string>
+
+// Small utility functions for common Wii related tasks.
+
+namespace WiiUtils
+{
+bool InstallWAD(const std::string& wad_path);
+}