Added ArrowObject position for its constructor.
Added collision_check(), on_tick(), on_collision() to BasicObject..
Added parameters obj2, id, distance to BasicObject.on_collision().
Added BaseObject.on_collision_middle() for "just passing by the middle of object" detection.
Added ArrowObject.on_collision_middle() handler - this is now functional \\o/
Updated ArrowObject and related textures to use the same direction ids as the objects (0: up, 1: right, 2: down, 3: left).