ERP5CatalogTool: Display view for portal_catalog when we access it on ERP5 UI

Before this change, index_html for Catalog Tool was None that means trying to access view for CatalogTool from UI always make a function call to the __call__ which function was overridden with searchResults, which means everytime someone tried to access portal_catalog/, a useless query was being made and an undesirable query result was displyed on the UI.

In this case, index_html is prefered whenever we try to access portal_catalog from UI.

Also, add test for proper display of view when CatalogTool is accessed from XHTML UI