New UFDS

Supported actions so far: FindSet(i) to see which set an item i belong
to; UnionSet(i, j) to link item i and j, if any; and Initialize(N)
disjoint sets. I need Rose's help to fix some minor GUI issues (can't
hide the input parameters for now). I also need Ivan's help to check
what's wrong with the first iteration at each animation? I will add a
few more features to this GUI if I have time, but otherwise, this is
already in a good state.