Simplify room ID for sharing

[kolumb]

It's scary for non-programmers and link will be shorter that way.

[sdegueldre]

I went with UUIDs because I wanted to be reasonably certain that someone could join a room with a stale link without having to add storage on top to track spent ids, but UUIDs are probably overkill for that anyway. I'm thinking about a word system like they did for gfycat or twitch clips, that way you could even type them in if for some reason you can't copy-paste them. I like the idea but this one is not obvious in what implementation would be better.