added a forest

-when the playscreen gets created it makes the forest
-treepositions keeps track of all of the positions of the trees
maybe useful?
-This function to create the grid of trees isn't very friendly, it
needs a lot of tweaking to make sure area's of the trees don't overlap
or we need to write something that won't let you chop two trees at once

-Also to make the game harder we should just scale up the time it takes
to chop a tree, get paper,then increase the health of animals