Updated __calc_path_preference to use Floyd Warshall

[eminberker]

The existing __calc_path_preference function in profile.py runs in exponential time (in fact O(m!)) since every recursive call can have up to m recursive calls. I am guessing this is the reason the chairs decided not to include __calc_path_preference in the profile initialization. The widest paths (i.e., strengths) for Schulze can also be done using the Floyd Warshall algorithms, which runs in O(n^3) time. In my local runs, this version __calc_path_preference runs much much much faster than the original version.