Major Update: PNPM, and merged Core, Python, and Electron into single repo (all BSD licensed now)

[williamstein]

I completely switched all of cowasm to use pnpm instead of npm. Since pnpm workspaces are vastly superior to npm workspaces, I also merged the cowasm-desktop, cowasm-build and cowasm-python repos back into this cowasm repo, and everything is part of a single monorepo.

Regarding building, this is a major change, since building no longer pulls any cocalc build artifacts from npm. This makes it much easier to test out doing the complete build in different environments, upgrade dependencies, etc. Also, everything is easily maintainable all in one repo.

I also merged the cowasm-desktop webassembly desktop app back into the cowasm repo and relicensed it BSD (it was AGPL non-commercial). This provides a desktop app with a WebAssembly Python terminal that is running under node.js and has access to the local filesystem. I think it works on macOS and MS Windows (which was tricky for me to figure out!).