Split up Application and Container

- Stop trying to implement Laravel's Application contract, which
  has no value for us.
- Stop inheriting from the Container, injecting one works equally
  well and does not clutter up the interfaces.
- Inject the Paths collection instead of unwrapping it again, for
  better encapsulation.

This brings us one step closer toward upgrading our Laravel
components (#2055), because we no longer need to adopt the changes
to the Application contract.

framework/core/src/Http/Server.php

@@ -73,6 +73,8 @@ class Server
             Flarum encountered a boot error ($type)<br />
             <b>$message</b><br />
             thrown in <b>$file</b> on line <b>$line</b>
+
+<pre>$error</pre>
 ERROR;
     }
 }

framework/core/src/Http/UrlGenerator.php

@@ -18,6 +18,11 @@ class UrlGenerator
      */
     protected $routes = [];
 
+    /**
+     * @var Application
+     */
+    protected $app;
+
     /**
      * @param Application $app
      */