made ObjectList double-linked to allow forward- and backward-iterating. its now a LI(F/L)O list.
added an iterator to iterate through object-lists. you can iterate forwards and backwards.
iterating forwards is easy: you get "0 1 2 … last"
iterating backwards is a bit tricky: you still get "0" first, but then "last … 2 1".
thats caused by the structure of the for-loop: you get the first element before the iterator knows if you'll increase or decrease it