Introduce new DI container

- Adding Friendica\DI class for getting dynamic classes
- Replacing BaseObject::getApp() with this class

src/Module/Admin/Themes/Index.php

@@ -6,6 +6,7 @@ use Friendica\Core\Config;
 use Friendica\Core\L10n;
 use Friendica\Core\Renderer;
 use Friendica\Core\Theme;
+use Friendica\DI;
 use Friendica\Module\BaseAdminModule;
 use Friendica\Util\Strings;
 
@@ -15,7 +16,7 @@ class Index extends BaseAdminModule
 	{
 		parent::content($parameters);
 
-		$a = self::getApp();
+		$a = DI::app();
 
 		$allowed_themes = Theme::getAllowedList();