Remove image_dir as config param

Should always live in www directory.

config.sample.php

@@ -8,4 +8,3 @@ error_reporting(E_ALL);
 include __DIR__ . '/vendor/autoload.php';
 
 UNL_TourMap::$url = 'http://localhost/workspace/UNL_TourMap/www/';
-UNL_TourMap_Marker_Image::$image_dir = dirname(__FILE__).'/www/images';