[extreme] buggy survival

Each player starts with 3 GLA buggies and 1 Jermen Kell. Like on AoD maps, waves of enemy units will be spammed onto the map. Your goal is to survive and destroy each wave with your buggies. When you lose a buggy, it won't be replaced, so be very careful with them! You can change the difficulty by setting the bot to normal, hard or brutal. Check the readme file for more info.