AbiathRPC - Save levels locally

If you're working on a leveling project with some people, it's great to have a centralized copy of the levels (on the AbiathRPC server), but you also need to be able to get the newest version so you can test your changes in a game. Today, I added an option to the RPC menu that saves the current state of the levels to local files. Its implementation is very straightforward; the only special thing it does is check for the presence of a GAMEMAPS file in the current folder and fill the suggested file names with that file's extension.