Release v3.1.0

• Fix for CustomKnight not working with MoreSaves's additional save files
• Filter skins in Favorites / Recents that don't exist anymore in the Pause Skin UI
• API Bug - Don't NRE when calling SkinManager.AddSkin during initialization
• New API method - SkinManager.SkinExistsById to check for a skin in the skin list

(this is an identical release to v3.1.0 , I just needed to fix the MR action)