Rewrite Save Data & Impl Save Data Dialog (#824)

* core: Rewrite PSF parser & add encoder

add .sfo hex pattern to /scripts

* core/fs: allow to mount path as read-only

* common: Add CString wrapper to handle native null-terminated strings

* SaveData: rewrite to implement full functionality

* mock value for SYSTEM_VER

* SavaData: backup features

* SavaData: SaveDataMemory features

* imgui Ref-counted textures

- has a background thread to decode textures

* imgui: rework gamepad navigation

* PSF: fixed psf not using enum class for PSFEntryFmt (was a standard old ugly enum)

- Add null check to CString when itself is used in a nullable field

* SaveDataDialog implementation

- Fix Mounting/Unmounting check of SaveInstance

src/imgui/imgui_layer.h

@@ -12,10 +12,6 @@ public:
     static void RemoveLayer(Layer* layer);
 
     virtual void Draw() = 0;
-
-    virtual bool ShouldGrabGamepad() {
-        return false;
-    }
 };
 
 } // namespace ImGui