Make PNG compression level configurable (#1684)

Co-authored-by: Caprico85 <Caprico85@users.noreply.github.com>

Author: Caprico85

lib/Varien/Image/Adapter/Gd2.php

@@ -205,14 +205,7 @@ public function save($destination=null, $newName=null)
         // set quality param for PNG file type
         if (!is_null($this->quality()) && $this->_fileType == IMAGETYPE_PNG)
         {
-            $quality = round(($this->quality() / 100) * 10);
-            if ($quality < 1) {
-                $quality = 1;
-            } elseif ($quality > 10) {
-                $quality = 10;
-            }
-            $quality = 10 - $quality;
-            $functionParameters[] = $quality;
+            $functionParameters[] = 9;
         }
 
         call_user_func_array($this->_getCallback('output'), $functionParameters);