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.

src/Database/DatabaseServiceProvider.php

@@ -24,7 +24,7 @@ class DatabaseServiceProvider extends AbstractServiceProvider
         $this->app->singleton(Manager::class, function ($app) {
             $manager = new Manager($app);
 
-            $config = $app->config('database');
+            $config = $this->app['flarum']->config('database');
             $config['engine'] = 'InnoDB';
             $config['prefix_indexes'] = true;
 

src/Database/MigrationServiceProvider.php

@@ -10,7 +10,6 @@
 namespace Flarum\Database;
 
 use Flarum\Foundation\AbstractServiceProvider;
-use Flarum\Foundation\Application;
 use Illuminate\Filesystem\Filesystem;
 
 class MigrationServiceProvider extends AbstractServiceProvider
@@ -24,8 +23,11 @@ class MigrationServiceProvider extends AbstractServiceProvider
             return new DatabaseMigrationRepository($app['flarum.db'], 'migrations');
         });
 
-        $this->app->bind(MigrationCreator::class, function (Application $app) {
-            return new MigrationCreator($app->make(Filesystem::class), $app->basePath());
+        $this->app->bind(MigrationCreator::class, function () {
+            return new MigrationCreator(
+                $this->app->make(Filesystem::class),
+                $this->app->basePath()
+            );
         });
     }
 }