'ElectreTriDiscordances' and 'ElectreTriCDiscordances' merged into one,
generic module ('ElectreDiscordance') and adapted to the new data
structure ('Vividict').

Temporary fix in 'comparisons_to_xmcda' - apart from sorting
alternatives and profiles prior to serialization, we need to sort
partial results (i.e.  per-criterion) as well (if present).