Frontend refactoring and misc fixes

* Split widgets into namespaces
* Widget init via cd.state/on-el-om
* Switch om widgets to hiccup-style
* Move rendering of dynamic content of var pages to frontend
* Fix bug where request body was being decoded twice
* Fix inital value of new example not showing in textarea
* Rename comments -> notes
* Render comments, examples, and notes on the frontend
* Use marked.js for markdown rendering