added factions_games_split, factions_centric

factions_games_split is like games_split, without date, with opposing
faction conserved. It's the stepping stone to factions_centric, a way to
conserve how each faction has done against every other. Total count of
games is thus doubled in it compared to games_history. For html/php,
just keep the faction_id you want and discard all other tuples. Does it
need to have the logo, color and name of all factions and parent
factions as well?