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

composer.json

@@ -45,7 +45,7 @@
         "matthiasmullie/minify": "^1.3",
         "monolog/monolog": "^1.16.0",
         "nikic/fast-route": "^0.6",
-        "oyejorge/less.php": "~1.5",
+        "oyejorge/less.php": "^1.7",
         "psr/http-message": "^1.0",
         "psr/http-server-handler": "^1.0",
         "psr/http-server-middleware": "^1.0",
@@ -57,7 +57,8 @@
         "symfony/yaml": "^3.3",
         "tobscure/json-api": "^0.3.0",
         "zendframework/zend-diactoros": "^1.7",
-        "zendframework/zend-stratigility": "^3.0"
+        "zendframework/zend-stratigility": "^3.0",
+        "axy/sourcemap": "^0.1.4"
     },
     "require-dev": {
         "mockery/mockery": "^0.9.4",