XCM Playground

[franciscoaguirre]

We should build an XCM playground, something like https://play.rust-lang.org/ but for building and testing XCM programs.
It'd be really helpful for builders in the ecosystem to approach XCM.

My original idea for this is to grab the xcm-simulator, or something similar, compile it to WASM, interface with javascript, and end up with a website we can use.
We might need to make some changes to the xcm-simulator that we'll use for this.