[1.0.4] engine.Highscores relies on party

[Zireael]

Copying the ToME 4's highscores code from Game.lua, with all requires, results in the game complaining that it's trying to index global 'party' (nil value).

It seems that the highscores, for some reason, depend on the party system introduced in module.

We (Seb and I) think it's a bug, as engine should not depend on optional stuff.