[Open Assets] Cut Multiplayer Stages (Cut levels from 2.1)

Here it is, my first public WAD and a WAD literally nobody asked for. I was scrolling along the wiki when I found out that a bunch of 2.1 multiplayer maps were cut. Now, by no means are these maps actually good, but I figured why not. I had a lot of memories with these zones, and I can't let them go.

Keep in mind that these maps are not updated to 2.2 standards, which means all the 2.1 level design flaws are still here, and there aren't any slopes. I got it to the point that these maps are fully playable in 2.2 and show no errors, but if something is broken, just tell me and I will fix it. I played through several minutes of each map with a friend and everything worked fine.

I hope you guys enjoy this!

Unless the dev team says otherwise, I guess its OK to be put in releases.

So I noticed when advance map is set to next, these stages aren't registered in the sequence strangely. But if advance map is set to random, there is a chance they can be selected.

In the gifs below, Granite Lake goes to Celestial Sanctuary.

But when Diamond Blizzard is finished it goes to Celestial Sanctuary instead of Granite Lake.

I've updated the mod to fix aa479758's issue he pointed out.