Registers a new game theme.
themes:registerNew({
id = "worldwar",
display = _T("THEME_WORLD_WAR", "World war"),
match = {action = themes.MATCH_VERY_GOOD,
fighting = 0.75,
adventure = themes.MATCH_GOOD,
horror = themes.MATCH_GOOD,
simulation = 1,
strategy = themes.MATCH_GOOD,
rpg = 1,
sandbox = 1,
racing = 0.75}})