Returns the full path to the directory where the game should store files that can be shared among other apps and users.
Files in the global external storage directory shouldn't be deleted when the game is removed from the system unless the target platform won't allow its persistence.
Windows: the same as GetResourceDirectory
Mac OS X: ~/Library/Application Support/<bundle-name>/
iOS: <NSDocumentDirectory>/ethdata/<processName>/
Android: returns the valid external storage directory, e.g.: /sdcard/Android/data/<application_package>/files