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 as it was in previous version of site, 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.