Template Engine with Subdirectory

- Use explicit root path for template engine
- Replace "__DIR__" calls in addons with subdirectories
- Fixes local tests, where call is made out of '/' and not '/vagrant/'

src/DI.php

@@ -383,6 +383,14 @@ abstract class DI
 		return self::$dice->create(Util\ACLFormatter::class);
 	}
 
+	/**
+	 * @return string
+	 */
+	public static function basePath()
+	{
+		return self::$dice->create('$basepath');
+	}
+
 	/**
 	 * @return Util\DateTimeFormat
 	 */