updated mean and sd to use gojee

we should also make them behave nicely with a poll endpoint. 

Also i think it's time we generalise blocks a little - I'm copying and pasting waaaay more boilerplate code than I was 2 months ago. I think with `gojee` and the more refined ideas we have about state now we could make a block interface and move a lot of the junk to behind the scenes.