tag manager: fixed error message when response is empty (simple_html_dom)

git-svn-id: http://www.pimcore.org/svn/pimcore/private/core/trunk@2600 1f8fe7d8-47f0-464c-8d0a-336f4953ab05
added default value to group and key names

git-svn-id: http://www.pimcore.org/svn/pimcore/private/core/trunk@2601 1f8fe7d8-47f0-464c-8d0a-336f4953ab05