Gaijin.NET Agent now optional

Due to our player's feedback, we have made Gaijin.Net agent entirely optional during a Steam installation (now you can decide whether you want to use it, or not). Please note, not using the Gaijin net Agent can lead to delays in updates, if Steam updates are switched off/or not efficient. We still recommend using our solution, it is essential to keep your game up-to-date to be able to play!