Archives: Implemented ExtSaveData and SharedExtSaveData

They will be stored in /extsavedata/SDMC and /extsavedata/NAND respectively.
Also redirect some APT_A functions to their APT_U equivalents.
Implemented the gamecoin.dat file in SharedExtSaveData in the PTM module.
Implemented formatting the savegame.
Retake a previous savegame if it exists instead of reporting them as not formatted every time a game is loaded.

src/core/file_sys/archive_extsavedata.h

@@ -0,0 +1,45 @@
+// Copyright 2014 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include "common/common_types.h"
+
+#include "core/file_sys/disk_archive.h"
+#include "core/loader/loader.h"
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+// FileSys namespace
+
+namespace FileSys {
+
+/// File system interface to the ExtSaveData archive
+class Archive_ExtSaveData final : public DiskArchive {
+public:
+    Archive_ExtSaveData(const std::string& mount_point);
+
+    /**
+     * Initialize the archive.
+     * @return true if it initialized successfully
+     */
+    bool Initialize();
+
+    ResultCode Open(const Path& path) override;
+    ResultCode Format(const Path& path) const override;
+    std::string GetName() const override { return "ExtSaveData"; }
+
+    const std::string& GetMountPoint() const override {
+        return concrete_mount_point;
+    }
+
+protected:
+    /**
+     * This holds the full directory path for this archive, it is only set after a successful call to Open, 
+     * this is formed as <base extsavedatapath>/<type>/<high>/<low>. 
+     * See GetExtSaveDataPath for the code that extracts this data from an archive path.
+     */
+    std::string concrete_mount_point;
+};
+
+} // namespace FileSys