Investigate using AvlSetInt for Adjacency Matrix

[Martin Sjölund]

Currently, our adjacency matrixes use a list<list<Integer>> structure, but the order of these integers does not matter. If we start using list<AvlSetInt.Tree>, we could do operations like join and intersect without expensive operations. We would also not need to use List.unique. For the comSubExp module, the use of a single line of an intersection call used more than 50% of the total used memory of the entire translation process.