Convert the Galaxy namespace to a class.
Decirculize Factions and CustomSystems a bit.
Move the static faction stuff to its own FactionsDatabase object in Galaxy.
Move the static CustomSystem stuff to its own CustomSystemsDatabase object in Galaxy.
Move Sector::cache to Galaxy class.
Move StarSystem::cache and StarSystem::attic to Galaxy class.
Remove forgotten cache from StarSystem.
Forward declared SDL_Surface is a struct not a class.
Merge remote-tracking branch 'lwho/cache_in_galaxy'