Zombie Fortress Battlefield ZFB_200408

A small fix that fixes the images in the economy building tab plus making the grain to drop a seed after it is cut down/harvested just like the tree so it will grow again afterwards without the need to replant. Coins dropped from grain are lowered.
So now builders can make tree farm and a grain farm. Grain grows faster than trees and may be a quick way to gather coins for either buying materials from the trader or buying kegs and bomb arrows, to defeat the portals!
I am planning in the future of making the game mode even harder by releasing more bosses depending on how many portals are left.

Files changed:
grainnursery.as; economy.as; grainnursery.cfg; grainnursery.png; grainplantstuff.as;