Allow to change Wii sd card path in config pane

Add a setting in the "Paths" config pane to select which file should be
used as wii sd card.

Source/Core/Core/ConfigManager.h

@@ -177,6 +177,7 @@ struct SConfig : NonCopyable
   std::string m_strApploader;
   std::string m_strUniqueID;
   std::string m_strName;
+  std::string m_strWiiSDCardPath;
   u16 m_revision;
 
   std::string m_perfDir;