quadtree class for efficient collision detection
inner static helper class
fully implemented rectangle-helper-class
some static field -> properties of the quadtree
entities have now a width and height for collision detection
fields of the quadtree
constructor of the quadtree

the level is how deep the quadtree is, 0 is the root
the boundaries are the boundaries of the quadtree or the node
clear function for clearing the whole tree recursively
helper function for splitting the quadtree or node
getIndex

determines in which node the entity is placed
insert method

inserts entity recursively in the tree
retrive method

gets all entities in the same node as the entity
now for every entity class which extends from abstractentity
bug fix
class description added