[feature] show total required amount to buy all creatures

[kambala-decapitator]

Currently the "buy all creatures" dialog only shows max amount that you can spend out of your available resources if you try to hire as many as possible. Would also be great to show the total required amount of resources to hire all available creatures, use case: I want to exchange resources on the market to buy the rest of the creatures, but I don't know the exact amount, need to calculate it manually.