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
- Register required permissions so that "start discussions without approval" can only be set for groups that already have permission to "start discussions" (and same for reply)
- Change the "hidden" trash badge into a more descriptive gavel badge for discussions that are awaiting approval
closesflarum/core#904
