See https://github.com/flarum/core/pull/1367
* 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"
* Restructure `less` directory
- Add a key to each list item so that Mithril's diffing algorithm is used correctly. This prevents the emoji images from remaining for half a second before they update to a new suggestion.
- Clean up styles. The `PostPreview` doesn't really belong here.
