Move Custom MP Gamemodes to the Custom "Game"'s "Difficulties"

[TheGreatAutismo]

Instead of having "Custom Hunt", "Custom Co-op", etc. as "games" in the multiplayer level select, just have "Custom" as the game, and list all the gamemodes under the "difficulties" instead. Also make it pull from the proper folder in platinum\data\multiplayer instead of only platinum\data\multiplayer\hunt