WIP add some bones and zaubertrank to site skeleton

This is basically what `jekyll new` generates with added jade sugar.

also has a demo on how to render stuff from the `_data` folder. that way, people can send PR requests to add their planned sessions and the site will update automagically after merge. we can also generate all kinds of print stuffz from it too (badges, voting sheets, agenda...).

Jekyll can do sass, but I could neither get the slim or haml plugins to work, so i added a gulp workflow for jade, moved sass there too to have all generating in one place and added foreman as wrapper. See Readme update: https://github.com/CSSunconf/CSSunconf.github.io/blob/2aaa2d17e656080d482ede8ed142dfe2ef024804/README.md

While I would have prefered to just clone another site, I couldn't find one fitting. the jsunconf site for example is based on wintersmith and thus can only be updated locally and then using a new build – which is sure to fail the minute it gets urgent.

@verpixelt I left out any production stuffz like auto-prefixing, minifying, etc yet – we can add it later. will also do some clean up later today or tomorrow.

:baby_chick: