Upgrade OC version 1.5.2.2 to version 1.5.6 + fix minor issues

On an existing OpenCart webshop we need the newest version 1.5.6. The webshop is now running on 1.5.2.2. The webshop has some extension which need to be updated as well. We will provide the new version of the extensions. The webshop should work in the newest version without issues. There are also 2 minor issues that needs to be fixed: - Search engine is not working (standard original OpenCart search engine). - Order buttons of the products do not work on the home page and on the category page, because the products have required options to fill in.