ModCallbacks.MC_PRE_RENDER_CUSTOM_CHARACTER_MENU has a unusable sprite argument

[Foks256]

This callback only triggers for custom characters, yet the sprite argument only triggers on vanilla characters, which means that it's basically useless, so I propose a replacement for the sprite argument.

Replace that argument with DefaultSprite (PlayerConfig:GetModdedMenuBackgroundSprite()) and add another argument for PortraitSprite (PlayerConfig:GetModdedMenuPortraitSprite()), two new arguments that would be really useful to have in there.