* Add extra feature to a11y focusring mixin
* Add visually hidden CSS class and mixin
* Visually hide checkboxes (keep in focus/a11y tree)
* Place checkbox focus ring around display element
* Improve mobile checkbox/switch accessibility
* Replace gulp with webpack and npm scripts for JS compilation
* Set up Travis CI to commit compiled JS
* Restructure `js` directory; only one instance of npm, forum/admin are "submodules"
* Refactor JS initializers into Application subclasses
* Maintain partial compatibility API (importing from absolute paths) for extensions
* Remove minification responsibility from PHP asset compiler
* Restructure `less` directory