CoCalc Updates

[williamstein]

I merged all of the pull requests and everything is live in production -- including hub, manage, and frontend (see https://github.com/sagemathinc/cocalc/pulls?q=is%3Apr+is%3Aclosed)

I also did a bunch of additional development on CoCalc today, which is now live in production:

• Cambridge wanted this public share to actually work and show a nice interactive 3d plot. Now it does. In general you can now share any .html files and they are not sanitized, but instead put in a highly sandboxed iframe.
• I removed all mention of Discord and instead pointed everybody to https://github.com/sagemathinc/cocalc/discussions. While I was at it I updated a lot of links to our old blog to instead point to Blaec's new blog https://about.cocalc.com/cocalcs-blog/ Our Discord channel just hasn't been as overall useful as I want.
• Fixed "nice links", i.e. when you put an internal link in cocalc in Markdown, it should get formatted nicely for display when you stop editing, e.g., like this:

instead of `https://cocalc.com/projects/369491f1-9b8a-431c-8cd0-150dd15f7b11/files/work/2022-10-10-all-hands.board`.