Achievement fixes

Some of you had problems with achievements not unlocking. This may be caused if the connection to Steam is not stable or if Steam is in offline mode. So I made a change that every achievement you get is "remembered" and in case it can't be sent to Steam, the game will try again at the next start of the game. You can now view the state of your achievements in the game under the stats in the main menu

Also, one special achievement should now be easier to get. ;)