Clean up GetEvals explode() calls

[guidopetri]

Right now the positions/evaluations/eval depths get exploded separately in GetEvals which causes a bunch of issues (namely, what happens if there is a position but no evaluation for it?). It would be far better to have these list-likes exploded together instead of separately, but I think this requires a restructuring of a bunch of the visitors code (or getting the game infos).