Frontend refactor (#1471)

Refactor Frontend + Asset code

- Use Laravel's Filesystem component for asset IO, meaning theoretically
  assets should be storable on S3 etc.

- More reliable checking for asset recompilation when debug mode is on,
  so you don't have to constantly delete the compiled assets to force
  a recompile. Should also fix issues with locale JS files being
  recompiled with the same name and cached.

- Remove JavaScript minification, because it will be done by Webpack
  (exception is for the TextFormatter JS).

- Add support for JS sourcemaps.

- Separate frontend view and assets completely. This is an important
  distinction because frontend assets are compiled independent of a
  request, whereas putting together a view depends on a request.

- Bind frontend view/asset factory instances to the container (in
  service providers) rather than subclassing. Asset and content
  populators can be added to these factories – these are simply objects
  that populate the asset compilers or the view with information.

- Add RouteHandlerFactory functions that make it easy to hook up a
  frontend controller with a frontend instance ± some content.

- Remove the need for "nojs"

- Fix cache:clear command

- Recompile assets when settings/enabled extensions change

src/Locale/LocaleServiceProvider.php

@@ -25,7 +25,7 @@ class LocaleServiceProvider extends AbstractServiceProvider
      */
     public function boot(Dispatcher $events)
     {
-        $locales = $this->app->make('flarum.localeManager');
+        $locales = $this->app->make('flarum.locales');
 
         $locales->addLocale($this->getDefaultLocale(), 'Default');
 
@@ -38,7 +38,7 @@ class LocaleServiceProvider extends AbstractServiceProvider
     public function register()
     {
         $this->app->singleton(LocaleManager::class);
-        $this->app->alias(LocaleManager::class, 'flarum.localeManager');
+        $this->app->alias(LocaleManager::class, 'flarum.locales');
 
         $this->app->singleton('translator', function () {
             $translator = new Translator($this->getDefaultLocale(), new MessageSelector());