Add ids to .workshopper divs, reformat some html

This PR will add the ability to link to separate workshops. Yes, this functionality won't highlight needed workshop as distinct, but it's a place to start. Further improvements might be done using `:target` pseudoclass.
ids were taken from [old data-urls](https://github.com/nodeschool/nodeschool.github.io/blob/0e1cd46db88c7716bd55a3894232387df4e17bfd/index.html) so that all old links people might have in slides/github will probably work (btw, current ids for learnyounode, streamadventure divs are different from previous verions). This PR also fixes formatting for 2 divs to be as for all other .worskhopper divs.