Replace Tinker with a "sell tank" option in No Tinker mode

[koshen]

if you want to buy a better tank and you buy a tinker first because you dont have enough money yet you will get half of the old tanks value back.
in "no tinker" you will get the pilot back, when buying the tinker, I think there is a message like "you cannot buy this tank in "no tinker""

+1 . You'll get half of your old tank's value back regardless of what you buy. We also might want to consider making the pilot vulnerable as buying a tank earlier than you can actually afford should incur some sort of risk to the player. If changing the pilot into an actual movable unit presents problems than we should replace the tinker that can be bought with one that has no skills.