QuadTree improvements
Arguments in public constructor are w and h in tiles.
for-loop to for-each-loop
QuadTree.remove(T) method
Added getMin and getMax methods to SpatialData
Improved QuadTree.remove(T) method
Improved QuadTree.add(T) method
Added getIndex(T) method to remove copy-paste code
Added a couple of useful private methods
Added query method to QuadTree
Added QuadTree<Creature> field to Area class