Copy the config.php file upon installation.

This allows us to know whether Flarum is already installed, so that
we can disable certain service providers when it isn't.

This should fix #67.

framework/core/src/Console/InstallCommand.php

@@ -47,6 +47,9 @@ class InstallCommand extends Command {
         $this->call('db:seed', ['--class' => 'Flarum\Core\Seeders\ConfigTableSeeder']);
         $this->call('db:seed', ['--class' => 'Flarum\Core\Seeders\GroupsTableSeeder']);
         $this->call('db:seed', ['--class' => 'Flarum\Core\Seeders\PermissionsTableSeeder']);
+
+        // Create config file so that we know Flarum is installed
+        copy(base_path('../config.example.php'), base_path('../config.php'));
 	}
 
 	/**

framework/core/src/Core.php

@@ -0,0 +1,9 @@
+<?php namespace Flarum;
+
+class Core
+{
+    public static function isInstalled()
+    {
+        return file_exists(base_path('../config.php'));
+    }
+}

framework/core/src/Support/Extensions/ExtensionsServiceProvider.php

@@ -1,5 +1,6 @@
 <?php namespace Flarum\Support\Extensions;
 
+use Flarum\Core;
 use Illuminate\Support\ServiceProvider;
 use DB;
 
@@ -12,7 +13,9 @@ class ExtensionsServiceProvider extends ServiceProvider
      */
     public function register()
     {
-        $app = $this->app;
+        // Extensions will not be registered if Flarum is not installed yet
+        if (!Core::isInstalled()) return;
+
         $extensions = json_decode(DB::table('config')->where('key', 'extensions_enabled')->pluck('value'), true);
         $providers = [];