Final UF works. Correct number of clusters.

The final UF correctrly replays all the merges. We got the final map of
all the connected components. The total number of them seems to be
correct, tested both on the dummy surfaces, as well from the 1k surfaces
from the GFMD simulation.

Next: 1) define min/max cluster sizes;
      2) calculate and print cluster size distribution;
      3) define whether there're percolating clusters for both periodinc
      and non-periodic BCs.