Survival Shenanigans - Asteroid Material Variety

Part of a series of mods I'm creating collectively referred to as the Survival Shenanigans Suite. This mod adds a number of vanilla planet-specific stone materials to asteroid generation and the two varieties of "alien ice." Approximately two vanilla gray asteroids should generate for every modded stone asteroid. Adding two types of ice on top of the stone results in about 50% more ice in asteroids overall, and the two new types are significantly more visible from a distance.